I'll never truly like AC until they improve the steering feel. The 458 is just so floaty feeling at low steering angles, for example, but all the cars are prone to wandering around the straight-ahead way too much.
I'll also never really get in to the online mode until they install some excellent pickup racing systems.
Oh, and whilst the topic is there, LFS circuits are excellent, imo. They fit the brief really well, the S1 tracks focused around the sorts of cars that came with them brilliantly. I never really loved Aston, but Fern Bay just captures that "style" of circuit so well, the layouts are excellent, and I would drive those tracks in any sim. South City is an excellent city circuit, and Kyoto Ring is an excellent Oval/infield circuit too. I don't care about real circuits in video games, or real cars, none of it's real so who cares? Laser scanning gives the circuit (hopefully) a realistic surface fidelity but it's still all polygons and pixels. I'll always prefer the narrow tight style circuits, and honestly I couldn't care less whether they exist in real life or not. I'd rather drive Fern Bay than some Tilke crap any day.