Picked up the GOTY bundle edition of this in the Steam sale; had my eye on it for a while now, waiting for a good sale price. Gotta say it's pretty awesome so far. Just been doing the Career mode in the Clio Cup and a few one-off races and tuning sessions here and there, but I've been very impressed. It's so much better than GT6 in most aspects.
- Visuals are just flat-out amazing, especially the lighting and weather effects. Driving into the setting sun is somehow almost as painful as in real life, and both bright sunshine and cloudy days look remarkably realistic; I was amazed the first time I noticed my dashboard's reflection on the windshield on a sunny day. Granted, you can't really fault GT6 for this aspect, given that it's made for an aging previous-gen console platform, but I think PCars is setting quite a high bar in the looks department.
- Sounds are also impressive. Admittedly I've only driven a few different cars so far, but they each sound completely unique in terms of both engine and drivetrain, and the engine sounds are beautiful even on my meh 2.1 PC speakers. The environmental sounds that I really liked from previous SMS games are also present here, which really adds to the immersion. Just no comparison to the GT6 vacuum-cleaners and sterile environments.
- The driving physics are awesome; a lot more realistic than GT6. I love that brake fade and cold tires are a thing, as are overheated tires that don't instantly cool down a hundred feet down the next straight. Even the little Clio Cup car in PCars is a lot less forgiving of poor inputs than most GT6 cars. The feel of the weight transfer and the physicality of the car is far better. Car damage is also far better here; it doesn't seem to be quite realistic in terms of magnitude (it seems harder than it should be to do significant damage even with full damage realism enabled), but you can absolutely screw up your car in all sorts of interesting ways (both visually and mechanically) by crashing into things.
- Controller support is also great. I'm playing with a Logitech F310 gamepad (basically a DS3-style controller, with similar analog triggers). The out-of-the-box controller settings were...not great, but starting with some popular suggested DS4 settings and tweaking a bit from there, I've found a balance that works well for me. The fact that there are so many control-related settings that can be adjusted is awesome, seeing as how most games just hide them under the hood. A huge, huge improvement on the PS3
Shift titles; I found
Shift 2 to be basically unplayable with a controller and there was no way to fix it.
- Car tuning is quite extensive, much more so than in GT6 (and the tuning actually works properly, even the camber!

). I like that you can adjust all of the right and left side setting separately (even if it does mean a godawful lot of sliders to fiddle with); that's quite handy for certain tracks.
- AI seems to be quite decent so far. Very adjustable; I started off at 50% by accident (didn't notice the AI setting in my first race) and was pacing the field by a few seconds a lap in a Clio Cup car with the default tuning. Bumped them up to 85% and now I can pull off a win at a track I know well
if I have a decent car tune and I drive a near-perfect race, but at unfamiliar tracks I'm solidly in the middle of the pack (as it should be). Without a proper tune, the 85% AI was outrunning me by a couple seconds a lap. The AI drives fairly reasonably; there are usually one or two corners where I can get a bit of an advantage on them, but in most turns, they're my equal or better; they don't brake way too early and drive too slowly for every corner like in GT6. They occasionally get a bit aggressive, and I've been punted a bit once or twice, but usually it's because I've ****ed up and braked too soon or cut down on their line when they had a head of steam. Mostly they're pretty good about racing with you, and you can run side by side without them mindlessly driving you off the track. Haven't driven in any races with faster cars yet, so I don't know if their behavior changes in other classes, but it's a far cry from the GT AI for sure.
Track count seems to be pretty close to GT6. I think PCars may have more real-world circuits, and they definitely have more variations on some of their tracks. Overall I'd call it a draw in that category, though PCars is probably the winner if you like real-world tracks.
GT6 obviously has more cars, of course, even discounting all the same-model duplicates. All of the PCars cars are high-def models, though, with unique sounds and driving physics, and they still have a great variety of different classes and types of cars (more than GT6 in some classes), though of course GT6 wins hands-down in the number of road cars available. I wouldn't have minded a few more normal cars in PCars, I guess, as I like bombing around in funky road cars, but there's certainly enough in the game to keep me satisfied for a while, I'd say.
The career mode in PCars seems OK so far, but it doesn't feel like the same progression aspect as the GT series or other games, since there's no monetary aspect or team management and no unlocking/buying new cars or upgrades. The plus is that you can jump into career mode at any series on any level, though; no need to grind up from karts or slow cars if you don't want to. I would have loved to see a more in-depth career mode, ideally something like
Dirt to Daytona, but that's more of a wishlist item than a flaw.
Haven't tried the multiplayer myself yet, so I'm not sure how that compares to GT6 (though I certainly hope it's not as frustrating an experience...).
Overall I'd say it's a must-buy if you like racing sims, especially for the Steam summer sale price.