Definitely.
The lack of different offsets for rims front and back really kills the look of some cars, especially racers, and no open-wheeled cars with exposed suspensions means we miss out on some great rides: Caterhams, Ariel Atoms, and the like. Not to mention Formula/Indy cars. I've been able to look past the shortcomings up until now, but for next-gen, there are really no excuses and I'm hopeful the new engine will do away with many of these holdovers from FM1.
Also, I hope the more mobile crowds and spectators in Horizon will find their way into FM5 with animated pit crews, grid girls, race fans milling around the paddock, etc. More race day atmosphere, dammit!
Off topic and a fairly minor detail, but the driver in the Horizon cockpit vids finally has a proper grip on the steering wheel-- no more Forza Lobster Claws. Yay.