Tribunal adds a smorgasbord of new content to an already huge game.
If you absolutely, positively didn't like Morrowind at all, then this won't be the droid you're looking for: Tribunal doesn't so much make Morrowind feel like a whole new game, ala Diablo II LOD, but is more of a constrained version of it. It's almost as if you can install the game, start playing, and see something that says "NEW SUB-MISSION IS OPEN!"
Given the fact that everything in Morrowind was intertwined and seamlessly integrated with everything else, it will come as a bit of a letdown to fans of the game that the expansion is more of a self-contained bonus mission. It's a rather long bonus mission, to be sure, but there is much less of the freedom – and pointless wandering – of the original. Some will view this as fault, some will view it as a great improvement. The more linear nature of Tribunal certainly helps to flesh out Morrowind's epic story in a more concise nature, for which those with short attention spans will be eternally grateful.
Still, those with short attention spans probably shouldn't be playing a game like Morrowind in the first place. Tribunal tacks on an estimated 20 or so hours to a game that already contains potentially hundreds of hours of play, and thus is not for the fickle minded gamer. Playing Tribunal is like reading the abridged version of War and Peace, only in this scenario, you are required to own the full version to read the abridged one. A good investment for fans of Morrowind, but it's not likely to win over those who can't see what all the hooplah is about.
-George