Of all the "Vs." series Capcom has released, "Marvel vs. Capcom" is the best - music included. There's a large variety of songs here, some techno-ish, others with that rock-n-roll feel.
All but two of the Marvel characters have their same themes from the previous games. Wolverine has a cool song which is fast paced and pretty wild even for him. Venom, who is new to the "Vs." series, has some sort of spooky song that is too strange for me. It's difficult to say whether or not War Machine's theme is new. I consider it a hyped-up version of Iron Man's old song from "Marvel Super Heroes". Other songs may sound familar. Spider-Man, Captain America, and Hulk all have remixed themes of their Marvel Super Heroes themes. That horrible theme of Gambit's from "X-Men vs. Street Fighter" has been touched up as well. It sounds 100 times better and I actually like it.
As for the Capcom characters, some themes are familiar, and some are completely new. The Street Fighter characters get their old themes back with the exception of Ryu, who now has an extended version of the original introduction theme of Street Fighter II! The surprises don't end there. Anyone who has played Strider or the Rockman (Megaman) series will recognize their themes. As for Morrigan and Jin, I can't really tell (I've never played Cyberbots nor can I say whether Morrigan's theme is from Vampire Savior).
Captain Commando, Roll, and the Hidden Character themes are all brand new. Captain Commando's theme has that heroic feel to it; it's pretty nice. The Hidden Character theme sounds boring and unoriginal though. It sounds like a reject from the horrible "Marvel Super Heroes vs. Street Fighter" soundtrack. The biggest surprise of the soundtrack is Roll's theme. It has actual lyrics! It's very short and loops twice in about a two minute period, but it's something I've never heard on an OSV soundtrack! It's one of my favorites on the whole CD. Another favorite of mine is "Theme of Chun-Li". This song is yet another remix of her Street Fighter 2 theme, but with a twist. This is where the techno comes in. It's just too cool to explain; suffice it to say this is the best arrangement of her theme yet.
On a last note, if you insert the CD into a PC CD-ROM, you can access a web page which takes you to Capcom's secret website (if you can read Japanese and figure out what the password is). It also contains the "Marvel vs. Capcom: Clash of the Super Heroes" logo featuring War Machine, Ryu, Morrigan, and Rockman, along with MIDI versions of their themes. There is also a MIDI for the introduction theme. A big plus, especially for MIDI freaks. Anyone who is a fan of Capcom and their games should go out and get this soundtrack!