If you like Metroidvanias, you can give Timespinner a try. It looks and plays exactly as the gba and ds castlevania games and it has a fairly nice story (for these kind of games, at least) involving time travel. I enjoyed it a lot.
Edit: sorry, I somehow overlooked that you asked it to be a free game as well. This game isn't free, but I don't think it is very expensive either.