Hmm as far as modern twin sticks I of course love Nuclear Throne and Enter the Gungeon. Brigador is looking really hot but I haven't played it yet - definitely one to watch. Gauntlet is pretty solid too (specially co-op). Infested Planet was a great game, really great mashup of gameplay. Hammerwatch is probably my favorite couch co-op PC game and it should be right up your alley. You've probably played or own a lot of those already though!
I am obsessed with the 16-bit era of my teen years and so if you do any retro gaming I also have many recommendations. Top of the list would be Zombies Ate My Neighbors, Soldiers of Fortune, and S.M.A.S.H T.V. (all SNES).