I bought this game a few weeks ago, and having finished one full year of career mode, the season challenge and most other modes I think I know enough to write a full review.
I've played half-distance Career races at the first 3 (of 4) difficulty levels, and found them to be set at very good intervals. The lowest level, amateur, ceases to be a challenge after a few races, but intermediate was a bit trickier for a while. I'm up to professional now, and find that to be rather more serious, without being so tough I feel like I'm always on the back foot.
The tyres work extremely well. When tyres are grassy or get gravel on them it does rob them of grip temporarily, and trying a wet tyre on a dry track or vice versa is not a good idea. If you look after your tyres then after losing time to someone who's gone charging off you can make yours last longer, make up the time as they post slower laps and then pass them during the pit stops.
Weather was a key, and great, feature of F1 2010 and the same applies to F1 2012. Sometimes it can rain on one part of the track but not another, and differing parts dry out at different rates too. Rain can be very light or extremely heavy, and this can make tyre choices difficult and very important, and the AI drivers can get it wrong too.
Crashing is always fun, but damage is limited in terms of the bits flying off the car. I think this is due to the FIA not wanting the game showing cars being smashed to little bits. The effect is that losing a front wing (entirely or just a little bit) looks great but a full blown crash will do more limited damage than might be expected (you can lose wheels).
Happily, the drivers aren't entirely realistic, as Maldonado and Grosjean don't crash all the damned time. AI seems to be significantly better than F1 2010 but could still be improved. Cars are generally good at getting out of the way when you're lapping them and the starts seem a bit less crash-prone.
The penalty system (on the default light-touch setting) is much improved. It's not perfect (I once got hit from behind and then got penalised for 'causing a collision') but the instances of undeserved penalties are far fewer, and you can sometimes get away with deliberately damaging another car (not that I would ever do that). The biggest problem with it coincides with the AI. When you get blue-flagged (meaning you have to move aside to let a car about to lap you past) if you don't do it very quickly you get a penalty. However, the other lapped cars know exactly how to do this and then pass you immediately, because they know exactly how many cars are lapping, where they are and so on.
The graphics are very nice. This shows up most especially when there's wet or changeable weather. Following a car in heavy rain now means you get spattered with the rooster tail (the spray of water behind an F1 car in the wet) which reduces visibility almost to zero.
The cars, of course, look very nice and the tracks likewise. Effects such as the dipping sun in Abu Dhabi or the floodlights reflecting on the cars in Singapore work very nicely.
Maybe I'm going mad, but I do think there's a difference between the engines of different cars. And this is a good thing.
The engineer, whilst often telling me what happened 3 seconds ago, has a decent, clear voice. David Croft excitedly explaining certain scenarios (in Season Challenge, for example) didn't do much for me, but I very much enjoyed Anthony Davison's track guides.
Hard to assess without sinking hundreds of hours into a game, but I'd say there's quite a lot. There are variable modes and numerous difficulty options, and the full season offers a great, and lengthy, challenge.
I would say that there's strong replay value. As well as bumping up the difficulty for the second year of a season there are quite a lot of different options.
Bugs and other issues
The frame rate is an issue. I did not think it was before, but in Suzuka (Japan) it slowed down significantly. Not enough to make the game unplayable but enough to dilute my enjoyment of it. It also slows down elsewhere, but usually it's not very serious.
The extreme speed of the sport also means that the race engineer (who I decided ought to be called Jeremy, as he was noisier than he was useful) often said things that were out of date. Not a serious issue, but it does jar slightly.
So, if I were to give it a score, it'd be 8.5/10.