Since, i'm 10th Prestiege on Mw2 and 15th on Black Ops, i'll give you my opinion on the two games;
Mw2: Yes, the perks on this, some were silly, some were well thought of, but they were all simple, unlocking attachments was fun and it was good to play with friends. I don't understand your comment of 'Some near impossible weapon challenges' as they were all very easy and simple. The hardest things to do were; ACOG -> Thermal with SMG's and FMJ -> Ext. Mag. Which, with enough use of the gun, isnt that hard in the end. Yes, there was always the problem of Cross-Map Noob-Tubes, Danger-Close and Stopping power, but that was what made the game ineresting. If someone was using;
Scavenger, Danger-Close and Commando with a Noob-Tube, and you had Slight of Hand, Stopping Power and Ninja on, you would easily win a battle close range, as long as you had the reflexes to shoot at them first. The guns were A LOT MORE BALANCED. They had the three main assault rifles, but they all had their down sides;
Scar-H was powerful, but had a small clip size and fire rate.
ACR was weaker then ALL assault rifles, had a regular clip size and a medium fire-rate.
AK-47 was the most balanced assault rifle, but they sway when you Aim Down Sight (ADS) was horrendous, meaning it was used less for long-range fire-fights.
The SMG's were all dominated by the UMP-45, which with some skill, you could out-do with an MP5K or an Uzi.
The LMG's were all very balanced. You either had accuracy with low fire rate, or high power with low accuracy. (RPD vs L86SW)
Sniper Rifles, clearly the two starting ones, (Intervention and Barret .50 Cal) dominated the guns here, but the addition of Quick Scoping sort of ruined the point of these. ALTHOUGH, Quick Scoping wasn't always as accurate as most people 'guessed'. And it was a good way to have fun and muck around with friends.
Then of course, there was the Riot Shield, easily the funnest thing in the game.
The combination of Shot-gun and rifle was great. It was a tactical choice on if you wanted that quick switch to your pistol, or whether you had the time to switch to your Shotgun (Dominated by the SPAS-12's range).
The game was then invaded by hackers and became boring to play after a while. BUT this was a good opening for people to start making clans for Mw2 since challenge lobbies were easily available. (I started one and we reached 3rd in AUS/NZ for Mw2 then we pulled out).
Black Ops: This game HAD a lot of potential. The removal of Stopping Power was a good choice, considering that you can now use 3 even perks. The perks were all changed around and new challenges were adding for getting the perks to Pro status. BUT some of these were stupid and made you want to shoot yourself sometimes.
Example: Get 15 flag captures in Capture the Flag. Sounds simple? Capture limit was changed to 3 per round, instead of infinate like on Mw2, but if that wasn't bad enough, you would have people sitting in corners next to the flag spot with Ghost (Blue perk, like Cold-Blooded) and a FAMAS, which was changed to fully auto. (The UMP of Black Ops)
The perks were thought out but needed a bit more thinking through. I have Triton AX-Pro's (Gaming headset worth a fair bit of $$$) and with the Ninja perk on, I can hear almost everything going on. On Mw2 Ninja was an 85% decrease in YOUR footsteps, with the advantage of not being seen by heart-beat sensors. On Black Op's Ninja = Silet footsteps and Ninja Pro = Silent footsteps, no callouts when reloading AND louder enemy footsteps.
Black Ops is infested with CAMPERS and PUB STOMPERS (I will get to them soon)
You have players, who sit there with Ghost, Slight of Hand, Hacker, Ninja or Second Chance (Yes, it's still in CoD), with Motion sensor, FAMAS Dual-Mag and high kill-streaks on. Sure, one or two here and there is alright, but when you consistantly get them, it becomes annoying as hell. It makes you want to give up on Black Op's itself.
Now, Ghost is; regular: Not detected by Spy-Plane (UAV). Now, on Mw2 having Cold Blooded meant that you were giving up Stopping power, the ability to quickly kill someone, on Black Ops, there's no difference, it's just pure advantage. Ghost Pro is the same as Cold Blooded Pro from Mw2.
PUB-STOMPERS:
Well these guys are just plain annoying. They almost ALWAYS have Flak-Jacket (Explosives don't kill you unless you're damaged), Slight of Hand and Ninja. They ALMOST always have a headset, like mine, and will rush or camp, with, you guessed it, FAMAS Dual Mag. They usually have a KDR above 2. The highest i've seen is 11, from one of the older Solaris players. (PS3)
Guns:
Assault rifles are dominated by:
FAMAS (Unlocked at level 14), Galil (Unlocked at level 20), both strong guns with high fire-rate. Then, AK-47 (Unlocked level 38) and Commando (Unlocked level 42 or 44[Haven't played Black Ops in a while])
FAMAS has a super high fire-rate and the recoil is controlable, only just. It is easily the most used gun in the game.
Galil has a clip size of 35, 50 with Extended Mag and has virtually no recoil if crouched. Usually a 2-4 bullet kill.
AK-47 once again, most balanced rifle in the game. Has decent power and decent recoil.
Commando is the ACR of this game. It is a variation of the M4 Carbine and has no recoil over medium distance.
SMG's are dominated by: MP5K (Unlocked straight away) and Ak-74u (Unlocked level 17) The AK-74u has a medium fire-rate but with Grip or Rapid Fire attatched to it, it becomes very powerful. It has been 'patched' multiple times because it used to be a 2-3 bullet kill, now it varies from 2-4 bullets.
MP5K is the most balanced SMG in the game. The rest either have small clip sizes or no recoil and high fire-rate, but extremely low damage.
Shotguns: These are now Primary Weapons;
Olympia is the starting shotgun that basically looks like it is shooting flares or confetty at the enemy. It's double-barrel and not used very often. It has 0 attatchments.
Stakeout: The is the Spas-12 of Black Ops. It has one attatchment: Grip.
Very unpredictable, can give you 1 shot kills or 3 shot kills. Pump action, short range.
Spas-12: No longer pump-action. Semi-Auto with Suppressor attatchment as it's only attatchment available. Variates from 1-6 bullet kills.
HS10: This is the Classified Shotgun. It becomes available once you purchase the other two shotguns above. It has the dual-wield attatchment. Semi-Auto with 4 bullet clip. 1-3 bullet kills.
Snipers:
Basically the only ones used are the L96A1 (Bolt Action) and PSG1 (Semi-Auto classified sniper).
Treyarc had made the game with no intention of allowing players to quick scope. Since then, there has been 5 patches in an attempt to fix quick-scoping. Quick scoping is now medium. You will land a shot 50% of the time.
LMG's, these are useless. The only useful ones are the M60 (Only one with a clip larger then 35) and the Stoner-63 (High fire-rate and Extended mags = very good gun)
Secondaries are dominated by the Python (magnum of Black Ops). Most players use it dual-wield and it ranges from a 2-4 bullet kill. If that's not being used then CZ75 (Full auto upgrade) is being used. (Remember, this is by MOST players, not all).
Perks:
BLUE:
Not very balanced. There's really only 3 perks people use: Ghost, Flak-Jacket and Scavenger. The other two are Lightweight and Hardline. Once again, these used to be RED perks, meaning the player no longer has a quick kill with stopping power. Now they are blue perks and no stopping power is needed.
ORANGE: (Replacing Red)
Dominated by Slight of Hand, because it is easily the most useful perk in the game.
Slight of Hand (Same as Mw2), War-lord (Two attachments, pro = two equiptment), Scout (Hold breath for longer, pro = quicker weapon switch), Steady Aim (Challenges for this perk and stupidly hard, pro = recover from knife lunge quicker) and Hardened (FMJ is now a perk. This gives you increased bullet penetration through walls, pro = less flinch when shot).
Green: (replacing yellow)
Evenly spread. Most people variate what green perk they use.
Second Chance (Last stand from Mw2, except pro = you can be revived and you last longer), Hacker (Enemy equiptment shows up as red on your screen, pro = you can hack it to become yours (Claymores, Jammers, Motion sensors, Spy-Cams and C4), Ninja (Silent foot-steps, pro = silent footsteps, silent callouts (When reloading) and enemy footsteps are louder), Tactical Mask (Take less damage from Flash and Stun grenades (now called flash and concussion) and Nova Gas (Throwable gas) doesn't affect you. Pro = less effect some more and enemies that throw flash or concussion grenades at you show up on your radar) and last but not least is Marathon (Increased running time (about 2x regular run) pro = unlimited run)
Equiptment: Frag, Semtex, Tomahawk. (Throwing Knife that doesn't stick into walls)
PRIMARY Equiptment (CANNOT BE REPLACED BY SCAVENGER): Spy-Cam, Jammer, Motion Sensor, Claymore and Tactical Insert)
Secondary Equiptment: Willy Pete (Smoke grenade that does a little bit of damage), Nova Gas, (Throwable gas IS NOT REPLENISHED FROM SCAVENGER), Flash, Concussion and Decoy (makes shooting noises and shows up on enemy radar).
I see Mw2 as being a more balanced and interesting game. Black Ops gets boring really quickly, because all you get is the same thing over and over. The same class set-ups, the same noobs camping in corners, the same everything.
Zombies is probably the best part of Black Ops, and in my opinion, it's a waste of time. You sit there for 4-5 hours, trying to get to a high round to show your friends, and one mistake and that's time wasted. No reward, just abuse for either going down, or not being able to revive the downed person.
Campaign is alright. I completed all the challenges for it in a weekend. Nothing special.
I will say this though: Mw3 and BF 3 are going to be massive competitors in the market. I would suggest buying BF2 and seeing if you like it. Because you don't want to go and buy Black Ops, hate it and then spend more money on Mw3 and not like it.
Feel free to add me on PSN, I will play some Mw2 with you as long as you're aussie or NZ.
Cheers.
). He also killed crawlers when everyone else told him specifically not to for numerous reasons (bathroom break, Box, perks etc). We then started an Ascension game (which #2 didn't have). And he send me a 'strongly worded' message. 
I got my PS3 in December of last year so WaW was already out and so was MW2
Cheers 
) I'd still play Black Ops often. 
