Great thread, subbed instantly. It's mentioned as a link in one of the OP posts, but I feel like profiling Deadly Rooms of Death, also known as DROD. Behold:
Yes. It looks like ass. Yes, it kinda sounds like ass too. Yes, the voice acting is clearly like 3 Swedish dudes recording into a 2001 laptop mic in a bathroom, but Jesus christ, this game will destroy you.
DROD is a long running (1995-present day) puzzle game series that presents itself as a top down dungeon crawler, but actually is the most complex turn based puzzle game ever. You move around with the numpad, and rotate your sword using the Q and W keys. Each of those movements takes a turn, which in turn enemies will also take one. All enemies use predictable, easy to understand AI, so you can always use the same solution on each level. But where the game really shines is when it uses it's near hundreds of systems and mechanics to turn each room into a unique clockwork puzzle, having you poke and prod at each nook and cranny until you piece it together. 5 full games, plus 15 official expansion campaigns, and an RPG spin off gives you plenty to solve and there's even a built in level editor with a community collection of over a thousand mini campaigns to play. A great starting point is game 4:
Gunthro and the Epic Blunder, a game designed for beginners. All the other games (except for the most recent one) and official expansions are available as DLC for the Steam version as well.