There is so much I loved about Nightmare Reaper that it may end up as one of my favorite games of all time. The loot collecting of Borderlands, light RPG leveling through mini games, mixed with the speed of Doom Eternal makes for one heck of a time.
The gunplay is great and varied thanks to the loot collecting aspect. Getting carried by a weapon for a few levels then finding something much stronger or unique helped to keep things fresh. All of the weapons handle well, are all worth trying, and each weapon type was fun to use and all the different abilities you can find add to the mayhem.
Level design was pretty solid as well. Tight hallways littered with explosive barrels, open spaces where enemies just feel like they never stop spawning, along with some challenges thrown in (destroying crystals that do spawn enemies forever until you destroy them) help to keep things varied as you get deeper into the nightmare. There were a few times where the layout of a level felt same-y and I think that was from the Rogue-like part of its DNA. Not the end of the world but it was felt.
The mini games offer a break from the action and offer something different but there was some grind involved. The Arena based horde fights (think Serious Sam) to grind for Jade coins was a fun way to kill time and if you can get through 10 waves, any weapon you collected can be kept or sold and turned into coins to help level you up. The old school Gameboy style mini games are going to be hit and miss for some and is your main way of leveling up. Grinding for the currencies to play these can be a real pain in the neck and make them more of a chore. You milage will vary.