On the understanding that this isn't a PC vs anything else thread, rather a thread pointing out that there's still a whole schooner of bugs in PC, I'm not sure on what aspect PCARS is a better game than any other driving game title you'd care to pick. Except Driveclub. Driveclub is awful.
Again, I'll insert the caveat that I've not tried it with a wheel - I don't have a PS4 wheel yet - but I keep hearing praise for the driving physics. Now that's fine as statements go, but let's go back to the average gamer again... It's not someone with a dedicated driving sim setup in their mancave, it's someone with a console and a controller in their bedroom. I'm not getting anything from driving with a pad that screams "you must go buy a wheel for this" - its just plain bad to drive with a pad, but not in the sense that makes you think a wheel would be better, just in the sense that it's bad. One thing that particularly stands out as odd is that if you contact the back of a car (or vice versa) in the middle of a bend, you both understeer off.
I'm driving with the AI at default setting (50% I think) and, to be kind, they're spanners. They can execute ridiculously aggressive avoiding manouevres in turns of the sort that are impossible in real life (which either suggests that the physics modelling is very odd or that the AI can avoid loss of control unerringly), but they're total numbnuts the rest of the time. There is an extremely odd behaviour they exhibit in crash situations when the way ahead is blocked too - which is only extremely odd in that it's pretty much identical to GT6's AI and GT6's AI is not exactly championed as a perfect example of the breed. They reverse for an unusually long time while swerving violently from side to side, with little regard for what's actually behind them.
Now what this all generates is... an arcade game in feel. The automatons you're up against feel like scripted bots rather than other drivers - and this may be no worse than, say, GT but it's certainly no better - while the driving feels like you're gaming the nuances of a physics system rather than driving a car, which is a lot more like Driveclub (which I got free with the console and even that's too much money for it) than Forza.
I don't think that this is necessarily a bad thing - I'm happily ploughing through the career mode (which is a good thing, but could have been so much more) doing a bunch of invitational races while I wait for the superkart season to start up - but there's nothing really grabbing me and screaming about how much better the game is than other offerings, much less compelling me to think about buying a £300 wheel for it.
Sure, the dynamic weather is... dynamic and all (of the 70-ish) the cars have a cockpit camera, but I'd not be that bothered by the absence of either of those things - particularly as weather only serves to change the surface friction and the 'average gamer' already has a pretty floppy driving experience. The tuning menus are nice and detailed, but this is an aspect I doubt that most people will go into that much. It's a good example of something being thought of and included, but not being thought through - it's far too complicated for people who aren't that into vehicle engineering and it'd be a lot better if there was also a simplified series of sliders you could use to grossly adjust car behaviour (say, oversteer and understeer at each side of the slider, and a slider for corner entry, cornering and corner exit; a gearing slider from acceleration to top speed - and so on).
I like some of the track inclusions too - Donington is good, Oulton Park is fine, big fan of Snetterton and it's nice to see what used to be Sears Point/Infineon again. I like that all of the cars are available to drive whenever from the start - as opposed to the 66 from 1,2xx you get in GT6. Oh and I've not tried online yet because I'm not really convinced of the merits of buying some PSN yet, but I'm sure that'll be the usual hit and miss mix of public cluster(bombs) and good private racing. GT6's online stability is a little infamously wobbly, so maybe that's somewhere PCARS improves notably?
Since some of you chaps rate it, I'll wind up the AI settings (on the bright side, you can do this) and wind down the aids away from the default average gamer - but if I were an average gamer, I'd have put it back on the shelf by now. The same's probably true of GT6, but that's still not really an argument for how either is a better game than the other.
But back to the bugs.
I've not had anywhere near the problems that @TT92 describes - just silly, niggly things like my car being beamed onto the grid and bouncing about or the AI creating a traffic jam at Monza short. My bugbear is mainly things that have slipped the QA net, but these aren't bugs per se now I come to think about it.
To fully appreciate pcars you do need a wheel... your not really going to be able to fully appreciate the physics with buffers build in for limited range of motion on sticks. But to be fair, I have one of those ridiculous setups (CSW v2, 3x screens, chassis, blah blah).
Pcars is my go to "sim" for training but I couldn't imagine playing it with a controller and I have hindreds and hundreds of hours on Forza and GT, both controller and wheels.
I also prefer the career structure despite its major short comings but it's at least a structure and not just list of single events.
I'm just mentioning this as I would be horribly frustrated without a wheel... Feeling the tires bite and ridding the slip angle is s real joy.
In your case I'd suggest getting a wheel, but not just for pcars, it will refresh all your racing games and feel completely new. That's a good bang for you buck if you look at it across several products.
On to other points, the AI makes crazy moves because it doesn't really notice you until your nose is up to the mid point of their door, so during late trail braking and you slide your nose in, the AI freaks out and does odd stuff.
Try turning up the AI over 60% at least. I think anything under 50 is likely not behaving as it should.
AI is on a simplified physics model, that was the only way they could get so many cars on track. But it's constantly being balanced. They have the same lateral limitations as the driver, but can get away with quick extreme motions that aren't as critical due to far fewer physics calculations.
If you've ever considered a wheel, nows the time to pull the trigger. But don't get a crappy one, get a decent one. There is a huge difference between a Logitech and the far cheaper and superior 911 gt2... If they are still supported on new consoles.