The fourth archive (aka stage) is my favorite, but they are all great. Archive four and five both took me a couple tries. I don't know about everyone else, but I can't play for score and go for 100% purification/items at the same time. Playing for score I can't get everything.
My best score is just under a million for archive one. I was third on the leaderboards when I got it last night, but that won't last very long given how new the game is. I was literally so pumped up from doing well and not losing my 8x multiplier, that after finishing the level I had to stop for the night because I thought my heart might explode. It's a testament to this game's greatness how it can be insanely intense, or somewhat relaxed depending on how you play it.
I am in love with this game; it is truly beautiful. I made sure I had zero exposure to this game before it came out, I wanted to keep everything a secret so it would have a greater impact playing through it. It's very similar to Rez at it's core, but at the same time there are many differences. It's about the exact length Rez is, but it has unlockables clearly presented that might entice more people to put more time into it. It also has a hard mode that will be interesting to try once I have gotten 100% on more of the archives.
I played for about four hours last night, and hope I have time to do the same this evening. I want to try the direct assault equivalent this game has tonight. (I think it's called the Hope Archive)
Also, I suggest turning off your lights, and wearing headphones when you play this. I started doing this with Rez and find it difficult to play any other way now. It's also a good idea to turn off the 360's pop-up notifications to not taint the mood of the game.