If you were left disappointed by the Tribunal expansion then rest assured. Bloodmoon is a true expansion for Morrowind.
Like Tribunal Bloodmoon doesn't do anything to alter the core gameplay in any way. The main difference is that enemies are often in groups now making battles much more of a challenge. Bloodmoon's battles are much harder then anything you found in your travels during the main game and you'll likely find yourself reloading many a time. The enemy AI is still the pitiful thing found across the board in The Elder Scrolls III but the addition of multiple enemies really does add (or in some characters cases create) a challenge. The new quests are generally good but they are mostly the same kind of thing you found before but the developers have tried their best to keep it varied and interesting which they do to reasonable success. The new faction and it's quests are particularly enjoyable with an interesting premise and some characters that you just love to kill.
Visually Bloodmoon is on the same level as Morrowind. The new island is north west of VVardenfell and is covered in pine forest and snowy hills. New environmental effects like snow and blizzards have been added. The effect is surprisingly believable and you get cold just looking at it. It makes you want to don some of that bearskin armor you'll see floating around on the natives. The island is dotted with burial tombs, caves, and other sites. Of main interest would be the new imperial legion fort where your main quests will begin. In the sound department there are new weather sounds for the chilly blizzards you'll push through but that's about it. Once again you'll find no new additions to that much too short score. Of note thought that just every quest giver will have different greetings as you progress through quests involving them. It's a nice touch in a game with no voice acting.
If you had any tech issues in Morrowind or Tribunal you'll probably still find them here. The imperial legion fort exterior is especially demanding on your system and you'll be treated to a short slideshow when you enter it's courtyard. It's without a doubt the most demanding area for your system outside of Vivic.
Overall Bloodmoon is a great expansion in just about every way. While it doesn't fix any of Morrowinds problems it does offer enough new content of the same quality and variety that made Morrowind great. If you were disappointed with Tribunal then rest assured, Bloodmoon is the expansion that you wanted. If you haven't played either Morrowind or Tribunal yet then get all three as Bloodmoon adds more premium content to one of the biggest games you'll ever play.