Jewel Drops 2 has 5 levels of difficulty: Relaxed with no timer, minimal gaps, no bombs; Easy with no timer nor bombs; Medium, which is standard or normal mode; Hard; Expert. Have not gone beyond Medium.
Music has a rhythmic beat that may get repetitive, but I play in short spurts, so that's ok. Am only on level 17 of Relaxed, but the game is relaxing so far with mild challenges to make it interesting (beat level with fewest moves).
Hated Jewel Drops as it wouldn't run smoothly for me on iOS 9.3, but JD2 runs well. I'd recommend.