Man, I love the singleminded drones downvoting me just because I didn't say this game is perfect. I still like this game a lot, I'm just saying it's got flaws right now.
-There are a lot of fun primary, secondary and support (big guns) weapons to use. The gun play is very fun. Cool weapon models, cool weapon SFX, cool VFX. Unfortunately, only the automatic shotgun and arguably the incendiary shotgun or SMG are viable at any difficulty past the beginner stuff since the ones I mentioned are the only ones with enough DPS and/or ammo reserves to be useful at that level.
-Support weapons are the big guns. All of them very cool. Unfortunately, at difficulty 5 and higher, your team encounters multiple enemies during each swarm wave with heavy armor - heavy armor that is untouchable except to a scant few weapons that can pierce that armor. GG no re if your team doesn't have a competent person bringing one of these. At the moment, the meta is just use a railgun for everything, not because it is overpowered, but because it is the only weapon that isn't severely undertuned.
-General difficulty balance: OK, so the game sells you this idea of being a badass space soldier who gets to slaughter hordes of bugs or robots, right? But at higher difficulties, the meta shifts from being DOOM guy lite into being scared little babies who need to stealth past all the enemies on each map in order to succeed.
There's more I could nitpick but those are the big balance issues imo. Like I said, very fun, but expect to be frustrated by bugs and balance issues the more you play.