Played this on the Xbox 360 (until EA switched off the servers) and genuinely believe it to be the best RTS I have ever played. For context, i am comparing it to the majority of the Command and Conquer games, Age of Empires and Star Craft, all of which I have played. I believe this game to be superior because of its excellent balance and variety of the many factions and units, spells, research, etc. There is also something about how it connects with Lord of the Rings universe, even more deeply than the films do, making the game light hearted, fun and serious, all at the same time. The mechanics of the RTS itself, with hero characters bringing their unique dimension, just make this RTS full of different, relatively easy to learn, ways to play. I read that the PC version of this game also allowed a player to create their own hero characters as well, which just expands on that awesomeness.
The campaign was a great in depth unique Lord of the rings story, but where this game truly shines is in the multiplayer and me and my friend sunk so many hours in to teaming up and battling people from the other side of the world. Because the game designers seemed to factor in Peter Jackson's film interpretation of the books, you feel you are playing an extension of that great film trilogy, with familiar looks and sounds. However, the game designers also brought more characters and units to life that exist in the books, but did not make it in to Peter Jackson's films.
The large number of the different playable factions are in no way a gimmick, existing as the different races, operating in completely different ways, with them being very well thought out and balanced for multiplayer.
I think GOG should bring this back because I truly believe it is in a league of its own for the RTS genre and because it is a Lord of Rings game that has been made with respect to the source material, it also brings a very rich universe to really enjoy diving in to.