I like Forza. 
I mean, it's a lot better than GT though that's not saying much. That said the car damage and attention to detail push Forza way ahead of GT for me and I find it fun. Haven't played since the first one on xbox though. Another great thing about Forza is that it rewards creativity and allows players to make and customize their own cars. That's really cool, as no other racing game does what Forza does in that regard. Putting it in the same class at GT is doing it a disservice imo.
Forza is in the same "class" because it's attempting the same thing GT is: Racing simulator.
Forza gains the edge in regards to trying to foster a community online. Something GT didn't really do even with GT Planet/fansites. The Livery Editor allows people to trade for really good art/liveries that the GT community simply doesn't want.
Drive Club seems to be Sony's answer to Forza since GT itself won't change. Though really, Forza dropped car clubs from 2-3 (it was brought back in 4?) so I probably shouldn't say it's the answer to Forza when Forza itself dropped features that the first had only to take 1-3 games to bring them back... :/
I'd like GT and Forza more if they embraced 'The Real Boring Driving Simulator' aspect. I play these game is the most boring way imaginable: by drive around on empty tracks in different cars to appreciate the differences and for fun of driving. I hate them for the careers, racing, and 'game' parts.
The racing itself is fine. The problem is racing rubber-band AI in addition to the grind/"simulator" aspect. Not everyone is into doing 5 races to make enough cash to get an F1 car to drive. The "arcade" is supposed to fix this, but no one uses Arcade mode since it doesn't open up gates to other areas and kinda gets boring.
Arcade mode should be a "sandbox" like you want, but the actual game itself should be slightly less grindy and more "game"-y, if you know what I mean.
