The cars are fun to drive, it has Nordschleife and you can race online.
The a-spec is short and uninteresting and not really even fun. In previous gt games I've always struggeled with not doing one more race before going to bed. "just one more"... In gt5 doing the a-spec races was a chore and I had to force myself do them. It is almost impossible to guess the right combination of tires, bhp and car choise for a good race. This is even more of a problem because in the races there is usually one rabbit car that is a lot faster than the rest so you need to aim to match that rabbit car and not just fill in with a car that has similar performance like the rest of the field.
There are some really awful design decisions like paint chips, not being able to save during endurance races, cars you need to wait for to appear in the ucd so you can do a race, museum, horrible prize cars and prizes, totally missed opportunites with content (Nordschleife, top gear track, most of the cars...) and almost total lack of gaming features (for some races you need a certain type of car but that's all) which makes a-spec repetitive and uninteresting. The menus are awkward and a lot of the time I find myself going back and forth watching the long loading screens and waiting stuff to happen. The leveling system adds nothing positive to the experience and feels like an after thought.
Cars sound pretty bad but look great, especially the premium ones. I'm not too bothered about the looks of the standard ones. Rather have them looking a bit ugly than not at all. I want to drive the cars not to look at them. Which is why I also find b-spec really awful. I never cared for the photomode so don't care about that really. Nice to have I'd guess. Graphics as a whole look pretty good most of the time. Shadows are jagged and sometimes the game manages to look really out of date too.
Track generator is kind of "is it really there" at the moment. You can't really use it for anything else than race against ai using the track you generated. Tracks made with it tend to be really long and have really exaggarated elevations. The ai is bad too.
The difficulty levels vary horribly too. A-spec as a whole is more of battle against boredom than racing. It can be challenging if you really put effort into finding a car and tuning it just right to make it challenging but it's still nothing more than about overtaking the ai cars as quickly as you can. some of the lisence test can be challenging and the vettel challenge is really the only challenge there is in the game. Seasonal events is a nice addon to the short list of events in gt5 but seem to suffer from the same problems as a-spec. The money from those helps with the grinding though which is another problem with the game. Getting the money to buy cars is all about pressing one button in b-spec or doing roundyrounds in one super easy race. Online is pretty fun but also limited and has few showstopper bugs.
I could go on to list negatives (even though I already did

) but I don't want to say it is a totally awful product or give the impression that I hate it. Of course I expected more from a gt game. I thought my expectations were reasonable (drives great, lots and lots of races, fun ai to race against and properly laid out events). 1 out of 4.
Driving is still fun and that's what really matters to me. And it has nordschleife. Plus it has updates coming which will make it better. But I can't really see it improving so much that I'd be playing it few months from now.
I wrote this as a short piece but after every time I read it though I rememberd more bad stuff that I wanted to add. I could still go on listing the "stupidities" but I stop here...
So I give it 75/100. If the cars weren't fun to drive and it didn't have the 'ring I'd give it 10/100.