There have been many games that have been ported over to the iPad or iPhone from other platforms. Many of these games don't play as well on the IOS devices because of lack of a controller, however there are some games like World of Goo that are better on IOS devices. I first played World of Goo on the Wii and was hooked right away. When I heard it was coming out to the iPad and iPhone I knew this was a game that I would pick up right away.
The World of Goo is a physics puzzle game, in which your job is to use blobs of goo to build a structure. This structure is built to get the other blobs of goo collected by leading them to a pipe. The game starts out pretty easy but gets challenging. The structures are built by dragging a piece of goo and attaching it to the current structure to extend that structure out. What you have to be careful of is not extending it too far without some kind of support. What you are tempted to do is build the structure out to get to the pipe with as few moves as possible however if you do this the structure will collapse. So you need to make sure that while building you also use some of the goo to build support for the structure. You do need to be careful not to build too much support though as to pass every board you need to collect a certain amount goo drops. If you use too many in support then you will not have enough to pass the board.
This game is a blast and is one of those games that even though it is a port, works better on IOS devices. There are several must own games and this is one of them. The app is $4.99 and worth it but it has dropped to .99 before so you might want to keep on eye on it for a sale.