The main thing is that I'm not having that much fun - it seems like there are quite a few problems:
1) Number of cars available by default. In GT5 there were over 50 cars to choose from for free. In this game, the number of "courtesy cars" is 20. Whole eras and classes of car are missed out. It's not a good introduction to the game when there is so much variety in there. I really hope there is some sort of unlocking going to happen when I progress through this, but somehow I doubt it. GT4 still remains the best way to do this, with the three earlier games also shining examples.
2) The number of cars on track. I thought everybody agreed after GT4 that six cars just isn't enough? It seems like in GT6 all arcade races have 6-10 cars on track, which is a step backwards from GT5.
3) Rolling starts. I hate playing catchup - and being so far behind just doesn't make for very interesting races, when you know most cars on track aren't really taking part in the race, and it's just all about the delta time to the leader. Also, having a rolling start just isn't representative of the majority of real life motorsport.
4) Computer opponent car selection. So I choose an SLS GT3, and the computer is using a Peugeot LMP? And this is on "beginner" level?? How is that even remotely matched? When you start 10 seconds behind, and even a perfect lap will lose you another 10 seconds, why would I even bother to try to finish the race?
5) Track selection could be streamlined a bit. I'd suggest having reverse or night/weather versions of the track under a secondary option, so that the selection screen isn't cluttered up with 40 icons you have to scroll through. I'd suggest not even listing the dry versions of a track when the variable weather versions exist. And the racing direction could even be an option under the "Track options" menu where you pick the time of day. It's a shame, because otherwise the menus and loading in this game are all a big improvement.
6) Record keeping. The modes are separate, so I don't want my number of wins or distance driven to be added together. Mine should still say 0 races entered, and 0 hours of driving time, because that's what I've done in my A-spec career, and yet it says I have driven around 1000 km. I did quite a bit of statistical analysis in GT5, and this will be much more difficult in this game.
Other problems remain, like always setting race length in laps - especially with doing a 2 lap race on the Nordschleife or SSRX, and then 2 laps on an arena or karting course is just stupid. It's been suggested many years ago than another option would be to allow distance (in km) or duration (in mins), and this should be the default. Luckily the number of laps in a race is set right before the race starts, so at least we don't need to dig into the options screen...