Maybe I'm doing something wrong but most of the guns I've got so far have felt very weak. Even if they have a cool feature to them, it'll still take almost all of it's ammo to kill one boss. And when ammo drops are scarce, it can make things pretty frustrating.
Drops in general have been spotty for me. Is there any trick to them? I rarely get anything after a room clear.
The more you play, the more you'll unlock better guns in the shop. And you'll also learn that some guns are better for clearing out rooms and some are better saved for boss fights. That being said, the game is very stingy with drops, too much so. It can kill your runs quite easily when you're not getting any keys and can't get any weapons/items. I'm hoping they patch the game to increase key drops.