well, since there are now improved ilasera, gronmir, yagashura, abazigal, and demorgorgon fights available on balderdash - thanks Kevin and David! I thought I would go through my current game of TOB and fight the unimproved, then download and fight the new battle and compare them.
I played a party of five through SOA - fighter/thief PC, korgan, viconia, edwin and haer dalis (leaving a spot open to get Sarevok in TOB). I pretty much did every quest in SOA and this party got pretty powerful ending the game with about 4 mil exp each.
Like I think everyone else, I found the original Ilasera battle to be an utter joke. Even with her "team" the battle is easy and unmemorable. I understand that the battle is kept easy so that a player starting a game in TOB with a solo sorceror can still win, but I found that with a solo new sorceror WITH NO SPELLS it was still easy - just turn into the Slayer.
The improved battle, on the other hand, is very satisfying and memorable. Right from the start Ilasera's team looks more interesting - she has a big crazy ogre guy, a cleric, a mage, and another fighter. They cast higher level spells than in the original battle and they are somewhat harder to take out. The mage casts sphere of chaos and some other pretty good spells.
Ilasera herself the most interesting part, however. She is an archer and is an excellent shot - she uses the different archer abilities on you which makes it an interesting battle. She also goes ethereal and heals herself. She is also magic resistant.
The battle as a whole is still not really hard, I won it the first time with no preknowledge, and then found it easier once i had some tactics - one thing i did was to cast power word blind on Ilasera. Because she is a ranged fighter she is useless blinded.
Overall I really like the improved battle - it is more interesting and it "feels" more like a TOB battle - lots of high level abilities and spells around, a magic resistant boss etc., and it is interesting to fight someone with the archer abilities.
There is different treasure and one thing I have a problem with is that the improved Ilasera does NOT drop a pair of boots of speed like the original does, which is kind of a disappointment and is almost enough to make you not want to do the fight.