There are currently 20 modes. Of those several are structured and several are sandboxes or high quality shooting ranges to learn the ins and outs of the 150+ guns.
The structured modes include a survival horror mode, a tower defense mode, an RPG mode and, the one I was referring to, a rogue like mode which has you capturing spawn points with permadeath, progress based weapon unlocks which are based on randomized pools of guns and progressively harder enemies. Super addicting.
The game is constantly evolving and took me awhile to get into and appreciate but I’m very glad I did and highly recommend it.