Well if we're talking opening sequences then the 2nd opening (D-Technolife) was amazing. It was nice to watch, brilliant music, and wanted to watch everytime on the next episode. So much that i got the MP3 of the full song the day it came out.
The first opening i disliked completely, it just sounded off tune and i just couldn't get the umph with it. Not to say that the sequence for the opening wasn't bad though.
The new one...hmm. Well it's a nice touch and such, but the music isn't as glamourous. Especially with the gurggling part of the song near the end which kills it straight off.
The endings...can't remember the first.
But the 2nd (i believe..) Houki Boshi which showed off a squad each episode, was a really nice song, which i got the day it came out. I love that song. Ahhhhh.
Happy people was...wierd. "Happy people, ooooh, Happy people, Oooh yeah heh, bowwww"
The OST is quite nice, i'm into the techno kind of touch of it, and mysterious darkness in some of the themes. The others are plain cooky. And the song with the english singer in it, which sound like pop...dear god that scares me..