The title theme is pretty much my favorite title theme of all time barring This Dull World's Unchanging Pessimism (but then again that's from HM so...).
As for the other songs, here be my brief opinions (grain of salt is totally in effect here):
Stage 4: Moody, fits well, I like it.
Stage 4 Boss: Not bad, very different from a lot of things I've heard before, random Theme of Eastern Story that doesn't need to be there but whatever.
Stage 5: Also moody, certainly a lot darker than some songs I've heard in Touhou. I never noticed the similarity to Higan Retour until someone pointed it out, so that's something.
Stage 5 Boss: Reminds me in terms of the mood of the song to Rigid Paradise, and it sort of ties in with the ridiculousness of the gimmick (which I don't think is that bad once you get used to it but until then it's a pretty good surprise).
Stage 6: Very simple and repetitive, it sets the mood but out of the three songs that share that melody, I don't like it as much.
Stage 6 Boss: This took some warming up to, but afterwards I really enjoyed listening to it. That melody shared between the songs is much more powerful here. Also, it's similar to PoDD's title theme? Uh... I'll take your word for it.
Extra Stage: Again, moody and damn well fits, I think this is a good song.
Extra Boss: ...Pristine Beat does not do it for me. It's an okay song, but it doesn't feel like an Extra Stage boss song at all.