I've used FL for some time. The capabilities and features it has is really advanced and has gone as far as get its recognition from main stream producers. If my memory serves me correct its been used in 'Love the way you lie' by eminem (ft Rihanna), Avicii and is used A LOT by Afrojack
The synths I really admired were Toxic Bio Hazard for FM/subtractive synthesis (Created some bomb-ass effects), Ogun for additive synthesis (if you are concentrating on high pitched effects) and Sytrus (most advanced) for an all-rounder.
The feature which I used most was Synthesizer Creation Features. I spent most of my time creating basic Synths using Synthmaker (almost going deaf at one time, since I was tweaking the dangerous stuff). Didn't explore all of its features though, but the features are literally endless, since you can define your own parameters (and go as far as create your own native VST plugins using the C++ programming language).
The only way you can get used to FL is to play around with the tweaking features. Start with the basics of 3XOSC synth. Basic, yet powerful.
Very basic knowledge of computer-generated signals would help a lot as well.