I started off my first season with a P90. And yes, the mags are the biggest and only problem I have with it.
a: they are a little awkward at first to load/unload especially with excessive gear on.
b: hi-caps get feed problems occasionally. (I haven't played too many games yet and only got noticeable feed problems that required attention in my last game)
c: the mags are big, really long. any sort of pouch on your waistline will have you drawing them to your shoulder to bring them out. I have a triple mag drop-leg pouch on the way, will report later as to how well it works out.
Otherwise:
17 rounds per second, bullpup, and being able to get as close to a corner as a pistol for firing in CQB?
eh heh heh
read up on the RS