interactions between the various mechanics in the games likely yield countless surprises, and let you build something considerably more elaborate than thesum of its parts..
The Puzzle Boy / Kwirk series of games is Sokoban-based, but has 3 different mechanics on top of that: turnstiles, pits (that can be filled by blocks), and blocks larger than 1x1. One of the things I love about it is that, each mechanic is interesting on its own, and each combination of mechanics results in levels with very different feels. Lots of puzzles with a bunch of mechanics try to throw tons of them into each level, and each level ends up feeling very samey. But judicious use of combinations can lead to a lot of interesting variety.