One of the downsides I've seen mentioned is magazine memory, i.e. having to combine half-empty mags but to me that one is minor. My biggest complaint so far has probably been the amount of time you need to spend bandaging yourself. I preferred Battlefield's system of having the medic toss a pack down for an AOE heal, and that may be how the medic class works (I've only played Engineer) but I assume there will be tons of tweaks and balances during the early access period and beyond.