The Journal makeover is the main reason to install Tribunal :)
In terms of gameplay, the main quests in Tribunal are more focused, tightly located and well-paced, with a handful of dedicated quest givers, thus minimizing travelling fuss a great deal, compared to the original game, where travelling is hell. I would say Tribunal is a breather for Morrowind fans who find quest-running in the main game tiring and chaotic, where your operations are confined to a more dedicated game area called Mournhold, compared to the intimidating map of Vvardenfell.
Combat is harder though, and you may need prized items from the original game to beef you up for the powerful liches and constructs here, not forgetting a god too. Some of the enemies use paralyzing effects, which brings a lot of frustration and pain, so stock up on resist paralyzing stuff. If you don't mind the linear quests, it's a good expansion.