After seeing the first film, I fell in love with the song "Hero" from Nicelback and immediately bought the soundtrack to the first movie. Buying a CD just for one song isn't too bright, but I ended up loving all of the other music even more than "Hero".
When I saw Spider-man 2, I fell for Dashboard Confessional's "Vindicated", but this time I actually listened to some of the other tracks before I bought the CD, and I love it even more than the first. Whereas the first soundtrack was more grunge-y hard rock, the second is more "emo", still with a lot of rock but with a few softer tracks. The changes that took place from the first to the second film are the same changes that take place in the soundtracks. There are also a few recently popular artists on this CD, like Train, JET, and Maroon 5, but the underlying tones in the music are the same. The last two tracks ("Spidey Suite" and "Doc Ock" suite) from the score are great too, tweaked from the original versions but with a similar sound.
Overall, the soundtrack is great. If you love the movie and you love the first soundtrack, you are guaranteed to love this one. There are so many great tracks, you're sure to find some you'll play over and over.