Some games that I haven't seen mentioned so far but are worth looking at:
Sonic games: Prospector, Super Straight, Mars Trek, Faces, Cherry Bell, Butterfly. There are others, but these all offer a challenge while having unique and interesting layouts/rules. They play similar to Williams EMs of the 70s while generally having better features IMO
2 inch flipper games (some with zipper flippers): 2001/Dimension, Target Pool, Nip-It. These are very different from modern games but all have a one-more-game feeling.
Middle pop games: Spanish Eyes, Fan-tas-tic. The layout on these is just so challenging.