This game drew its influence from the various incarnations of the X-Men characters. The storyine was inspired by the original X-Men comics. The uniforms were taken from Ultimate X-Men (an alternate version of the comics created for readers who didn't want to have to deal with the thirty plus years of backstory from the original comics) and the design of the Xavier Mansion is taken from the X-Men film franchise that was introduced in the first X-Men (2000) film.
This game features a roster of 15 playable X-Men characters including: Wolverine, Cyclops, Storm, Iceman, Jean Grey, Beast, Rogue, Nightcrawler, Jubilee, Magma, Gambit, Colossus, Emma Frost, and Psylocke. Professor X is only playable during sections of the Astral Plane missions. The character choices for the X-Men were based on a number of factors, including character popularity with the fans, mutant powers (and their potential effect on the gameplay, visual elements and the story), and personal favorites of the development team. Other characters have never really gotten "their due" in games prior to this one and the creative team felt they deserved a chance to shine.
And addition to the story in the game are flashback missions which become available when talking to specific characters at certain parts of the story in the X-Mansion. There are a total of 3 flashback missions including: One where Nightcrawler talks about a time when the X-Men (in their classic 70's comic costumes from Dave Cockrum's art) had to stop a bunch of Sentinels, One where Beast describes the time the X-Men (in their original 60's costumes by Jack Kirby) had to stop Juggernaut from crashing through the X-Mansion in search of his step-brother Charles Xavier, and One where Wolverine talks about how he broke out of the Weapon X facility (with his wired helmet and battery harness look by Barry Windsor-Smith from the comic story) after getting adamantium grafted to his skeleton.
Angel was also to be included in the game, voice actor André Sogliuzzo is even credited as portraying Angel in the credits, but was cut from the final build. Despite this, Angel's model files and icons exist in the game's assets.