I've completed a large chunk of the game. Beat The End's light world and played a tiny bit of Cotton Alley. Unlocked all but four characters. I've completed 100% of Worlds 1, 2, and 3, and I'm currently working on 4. Basically, I'm just going world by world now, finishing everything in each one before moving on.
This game is really fun and satisfying. It provides and interesting combination of enjoyment and frustration (pleasure and pain). I was nearly addicted today, and had to force myself to stop. Sometimes it hurts to play this game, yet I always need more, and always need to finish what I start. It's like gaming crack, honestly, and I haven't experienced a game like this for a long time. You can say I was addicted to, for example, Super Mario Galaxy 2, but that was in a bit of a different way.
Obviously, playing SMB reminds me of a couple of years ago when I played through Jumper and Jumper 2. Those games were addictive for me as well. I'm just the kind of guy who loves platforming games, and I do have a soft spot for the challenging ones.
Also, I'm still loving that I paid just 10 dollars for Super Meat Boy. Such a great value.