I just beat the single player last night, and I think it's fantastic throughout. Aside from a couple one-hit kills (I probably should of been going slower anyway), the game is expertly crafted and the various fluid and light dynamics come together to create a challenging and fun experience. Q-Games really fine tuned the controls to be perfect and precise. 
 
All of the boss battles are great, but during the last one I kinda wished there was a checkpoint somewhere in the middle of it. I died about 20 or so times on it, but once you beat it you really feel like you've accomplished something.  
 
Good boss battles, we need more of these in games.  
 
Also, like almost all PixelJunk games, it gets hard towards the end. Not just the end boss battle, but the levels preceding it are challenging as well. The game gives you your limitations and keeps manipulating them to fit the situation at hand while never feeling beyond your means. 
 
So what I'm saying is that I really liked it, and for $10 it's a steal  
 
Buy it.          

I got the first one and I really loved it, haven't gotten this one yet because I wanted to see what people said about it but I think I'm going to download it this weekend. Only thing I want to know is about how long is the single player?

I've rescued all every survivor and found all the treasure. Needless to say I really liked the game. The last episode was a bit of a pain though.

I have 205 treasures. So, no I have not got all of the treasures yet. I plan on going back and rescuing everyone while looking for treasures in the future.  
 
I never got all of the treasures in the first pixel junk shooter either. I got of the treasures in the first world, then quit looking in the second world after not being able to find them.  
 
Unlike the first one though, I might have to force myself to do it just to see what the special surprise is.