Are any of the new fixes of the "must have" variety?
Well, some are pretty significant. This link contains a detailed list of all changes:
Known Issues - version 2.00 - Spellhold Studios
Here's some, off the top of my head, that I think are most important:
1) Morale, which was previously totally broken, is fixed. This means, among other things, A) your party will now be subject to fear spells, previously they were immune which made several fights against mages trivially easy, B) PC's morale will no longer reset to 10 after every 8 game hours - this means Dak'kon gets to keep his high morale Streaming Blade now (or Kinstealer, if you were being nasty to him instead) and some of his dialogue will reflect his higher morale. C) The stats on the various blades have been tweaked, as they were kinda nonsensical before, though it didn't matter because you couldn't really keep them without a lot of metagaming knowledge. D) NPC's affected by fear spells will now actually do what they're supposed to (80% run away, 10% panic, 10% berserk), rather than just standing there allowing you to easily AOE and/or kill them. That bug made 2nd level Horror more effective than most 9th level spells.
2) Most locks in the game were previously set to trivial values, so much so that you could bash most of them with a mage with 9 strength. They will have reasonable difficulty levels now (nothing Annah with a few points in Lockpick can't handle), and having the prybar equipped will give +10% to bash skill, as implied in the item's description. Getting through the mortuary at the beginning will actually require a minimum of thought now.
3) Expanded journal. The diary version of your journal could previously only hold up to about 128 entries. It will now display all entries all the way up to the end of the game.
That's some of the more significant stuff for the fixes. IMO, the new UB components are more "must have". Three components are brand new or greatly expanded.
1) Restored Sounds and Banters gets a massive update. 27 new voiced flirts between Morte and female zombies, using unused sound files. Also, 15 new fully voiced PC-PC banters, also built up from unused sound files.
2) Restored Mebbeth. Two dialogue segments in Mebbeth's dialogue that were previously ungettable, both including journal entries attached, though no quests.
3) Expanded Deionarra's Truth mod: There was a good deal of unused dialogue in the game that was ungettable because logically it required knowing Deionarra's ultimate fate before you actually learn it in game (and once you do learn it, you couldn't get back to Sigil to have those dialogues). This bothered me enough that I created a fairly sizable quest mod that allows the player to find out what happened to Deionarra before you reach the Fortress, and so can talk to her father about it (and that restores some dialogue with Yves as well). This mod includes roughly 180 brand new lines of dialogue written by yours truly, and restores about 30 lines of original dialogue once you've completed the quest and gotten the knowledge you need. I had what I think are some really good ideas for the quest, and I think it blends in -really- well with the existing content (and gives at least one existing quest chain that previously dead-ended some sense of closure).
Can I install them in the middle of my current game?
No, not this time, afraid not. It involves a lot of engine fixes and other major stuff. I mean, it's theoretically -possible- you could continue a save game, but I wouldn't bet on it going smoothly and I won't be supporting it.
Qwinn