Wicked Hard
There really is only one downside. I must clarify that I am a platform fan, and in saying so, have probably played about 40 or 50 platform games. The problem here is how incredibly hard and unforgiving this game is.
The difficulty starts out easy enough, but keeps on building, and building and BUILDING. If you read the GS review, they will indicate that there is a cheat to make the game playable - and it's true. Without the GOD cheat, I do not think it is possible to actually finish the game. The requirements to stay alive and in almost constant motion is obviously possible, but I would venture as impossible except for those with cybernetic implants.
Regardless, the game is a must-play for anyone who loves platform games, and is a great deal of fun!