Hi Andrew, like the previous reply, it depends on what you like. I have created a hub on the best apps and there are some games included in there.
I really like Temple Run (you control a little dude who runs through a bit of an obstacle course - highly addictive though), Bebbled (match coloured bubbles), Jewels (match jewels), Abduction! (steer a cow that jumps up on platforms) and Flow Free (bit of mind training - make sure that all 'pipes' flow free in this game). I tried playing The Sims but it demanded too much involvement and everything happened in real time so I thought it was incredibly slow.
I never pay for any of my apps so all of the above are free to use. Have fun!