I've beaten the game countless times, even on Monsoon, and have no plans to stop anytime soon.
This is easily the best shooter roguelike I've ever played, maybe even best roguelike overall. The game allows you to have a completely stacked arsenal of items. You can completely break the game this way, and it's so satisfying every time to get the items you want and start obliterating enemies you were previously struggling to keep up with.
Every character is so much fun to play with, and so unique in their playstyle. The levels never change their layout, but that's not really a problem, as your map knowledge helps you to clear stages faster, and the levels are large enough and with enough secrets for it to not be an issue.
The soundtrack is one of my favorite soundtracks, and easily one of the most fun to listen to front to back.
The DLC is totally worth it too!