Awesome game. I got it right at midnight the day it came out (and it took me 8 hours to pull myself away the first time ^.^; )
The first four stages are fun, but a little short if you ask me. You can breeze through them very quickly if you know what you're doing. Of course, you could always take your time and explore in those stages. I just felt like they weren't as massive as they could have been.
...this viewpoint of mine was quickly shattered when I reached the "Space" stage.
Space is big. Really Big. Really really REALLY Big! You just wouldn't believe how mind-boggling big it is!!!!
But all in all, I seriously suggest this game to people. Just hope it doesn't make you quit heRO!