re: cease and desist....actually, Epic isn't involved other than it's there engine and game being used for the mod, and they support all modders. Unreal 2 was developed by the now-defunct Legend Entertainment. Some of the guys working on this mod also developed the U2:XMP Bonus Pack Maps and, from what I gather, are working very closely with the original members of the team at Legend that developed the XMP expansion for U2. They received permission from Legend to use all the XMP assets in the making of their UT2004 version.
One part I don't understand is that Atari, the publisher of U2, hasn't lowered the boom, but they probably don't care because the game gets used in UT2004 which they get a piece of anyways. If it sells more copies of UT2004, I'm sure it doesn't matter to them. And it's not like U2 is selling like hotcakes these days.
As for "why all the fuss", XMP has a small but zealous community (cult?) following. It didn't really catch on so much over here, but from what I gather, the game is still pretty big in Europe (strange, because the same thing happened to another class-based team mod, Quake 3 Fortress. Hmmmmmm....)
Anyways, a lot of these fans felt cheated by Atari 'cuz they (Atari) didn't really support the product (UT2004 was making all the cash) and when they canned Legend, they canned support for XMP. (The game doesn't even have a master server anymore, you have to use Gamespy or All-Seeing Eye to find servers).
With XMP being ported to UT2004, these fans (Tek and myself included) will get a chance to play XMP on a much better engine (XMP's vehicle physics left *much* to be desired) as well as tap into a larger installed player base to support the mod.
There's also the gameplay itself. I strange hybrid of domination and capture the flag w/ vehicles, plus the different classes, the game mode pulls in influences and game mechanics from a number of different places (Tribes, Team Fortress, Halo, UT) and combines them into a fresh and unique game. And you can't deny the pleasure of jump jets.
Unfortunately, it just got over looked because U2 was so widely critically panned as a single-player game by players and press alike, and no advertising dollars went into promoting the new multiplayer expansion (although they did re-release U2 as a "deluxe edition" which had XMP packaged along with the original game).
So there you go....