If you're using a big screen tablet, there's nothing
I can recommend more than Machinarium
by Amanita design. It's an absolutely gorgeous indie puzzler which really had me scratching my head in parts, and it's got some of the best art I've seen in this kind of game.
Unfortunately it seems to require a large tablet; I purchased it when I had a Samsung Galaxy Tab 8.9 but when I upgraded to Nexus 7 it said it wasn't supported.