If you get very low FPS on some tracks (around 10fps) such as Abu Dhabi, and you are on AMD, then download latest 15.7 driver which fixes that.
I also had an issue with the game keep switching back to the desktop. Solved that by removing the custom Logitech Profiler profile I had for F1 2015 and instead set the global wheel settings only. (I'm using a G27 wheel). I also made sure my screensaver was set to only kick in after 240 minutes. One of these changes fixed the switching back to desktop and/or windows lock screen for me.
I'm running with 900 degree wheel rotation and using steering saturation at 65% in game to run with something close to 360 degree rotation in game, which seems 1:1 with the wheel movement in game.
I've had to lower environmental feedback to 10% with the other settings at 90% (wheel weight and force feedback iirc) otherwise the wheel clips like crazy when going over the grass, kerbs, gravel.
I think it's a great game, it runs at 60fps constant at 1200p on my aging 7950 with close to ultra settings, think I have just lowered vehicle reflections and shadows by one notch.
The driving feels really good, but these high torque F1 cars are a nightmare with traction control fully off. I'm getting better though. The only assist I have on at the moment is ABS, whilst I concentrate on getting used to manual gears (always used automatic in the past, but felt it was time for a new challenge).
The Singapore circuit in the rain really shows off the new engine. Previously I had always been disappointed with the graphics, especially on the Singapore track, in the previous F1 games.
I'm not personally missing the full career mode, as I tend to just do quick races and time trials. I can see though why some people are disappointed at the lack of features that had been included in previous F1 games.
Still I hear that the F1 dev team at Codies are only a very small team these days, so what they have achieved here is excellent and I only hope they build on this new better foundation for F1 2016.
Cheers
Mort.