30fps was expected, and to me is a good thing as it will allow them to push the graphics for the game. While 60fps is important for sim racers, for an open world arcade racers such as FH, 30fps is fine.
While Forza 5 has some amazingly detailed cars, you can tell the game suffers from them pushing for 1080p/60fps with a lot of low poly environmental models, and of coarse the fact that the lighting (while good) is baked in rather than dynamic. 30fps should allow them to really make the game look stunning.
Also, a lot of people here are comparing this to Driveclub which I feel is an unfair comparison as DC is not an open world game, and was delayed a whole year which has obviously allowed Evolution more time to fine tune the graphics.
If you are going to make a graphical comparison, then I feel that The Crew would be a much more fair comparison to make as it is an open world car game that will run at 1080p & 30fps, and should be coming out in the same timeframe as Forza Horizon 2.