Monument Valley is indeed very good, but you can beat it in 2-3 hours so it's more akin to watching a movie than having a game you can play a few minutes per session several times a day.
Tiki towers was also good. I haven't played enough recently to have too many more, but I would recommend Cause of Death (not on app store anymore, can download from hipstore and copy episodes over on a jailbroken device), as a text based game that was really well thought out.
Of course, you could always get a Gameboy emulator (even not jailbroken, Google it) and play whatever you want from there.
I also recommend the port of Bike Or Die, which was all the rage in the Palm era when I was growing up. Ios version is OK, although I'm not sure if it's still on the app store. You can probably find an IPA though.
True. The puzzles were and still are fun, just wish there were more of them. Almost makes me want to program a clone, allow people to mod it, just to play some more of the same-style puzzles...