It makes them feel different from other fights so it does add something.
I guess I wasn't specific enough in my wording. Change it to "adds nothing of value versus replacement".
Exploding barrels are a thing to prevent before they're placed or to run away from and/or explode to take out surrounding goblins while dealing with other kinds of enemies.
The problem with them is twofold. First off, the value of a "free" fireball at the level they show up in as too good to pass up. There really isn't a lot of added complexity on account of the barrels; the best choice is almost always to turn the barrels against the orcs (except during the half-baked stealth section) with some fire arrows. Second, it doesn't square well with the Infinity Engine's weaknesses in gauging blast areas. Designers should play to the strengths of an engine and certainly not build things on top of the weaknesses.
For Sherincal you either switch to ranged weapons and spells to finish the fight or deal with at least one round of having someone preoccupied with shooting the switch.
Basically what happens is that melee-oriented parties have to hit some stupid switch and any party with somewhat decent ranged attacks basically just bombards Sherincal and her caster friends with projectiles and magic. The gimmick of the encounter only effects melee parties by shutting them off unless they flip a switch. Not much in the way of complexity or multiple lines of play. Just a boring, poorly-done gimmick.
If they maybe implemented multiple "shields" for other types of attacks, the encounter might have had a bit more depth. It still would have been gimmicky, but a more interesting gimmick, with a bit more player choice involved within the encounter.
Oria's a gotcha for the inattentive/non-explorers.
Seeing as you basically have to explore the entirety of the Ice Temple and to get to Oria requires using the switches in the Battle Squares room (which includes the "lol, turn me ethereal" switch)...it's pretty bad "gotcha" design. Two ways the encounter could have been a bit better:
-One could make Ethereal Oria difficult, but not impossible, if you don't go to fight her while also in an ethereal state. Sure, it's not exactly original design to make a tough opponent that can be reduced in strength through exploration/environmental interaction, but it works and might even serve as an extra challenge for more advanced players.
-Make it so the party can sabotage something that causes harm/death to beings entering the ethereal plane from the temple. That way once you beat Oria and she breaks her staff, she can just die on the spot and you avoid the tedium of walking back to the other end of the temple, hitting the switch, and then going to put Oria down.
I like enemies with stuns and a one-round stun isn't all that powerful unless they're constantly going off, which she doesn't do (at least on normal and hard).
I'm none too fond of party-wide stuns without saves. They tend to encourage/legitimize the "load up on buffs beforehand" strategy. Said strategy is most unavoidable in RPGs that allow spellcasting/buffing outside of combat and have non-randomized content, but I feel it's better swept under the rug, where players can find/use it if they so choose. I don't like how Holy Word style spells, used against the player, take it out from under the rug and put it right in the middle of the living room.
My main issue with the encounter, however, is how the difficulty of the encounter greatly varies based on the alignment composition of the party as being Evil basically disarms the Twin's most dangerous ability. Alignment hosers should never be so high profile, yet the IWD2-cru put one in the final boss fight.
I consider IWD2 and BG2 roughly comparable in quality though I'll grant that BG2 is more consistent overall. Bioware had 18 months to make their sequel whereas Black Isle was given 4-then-10 to make theirs.
That's an incredibly rough comparison. There's nothing in BG2 that is as poorly done as areas like Dragon's Eye, the Ice Temple, the Monastery; areas that really couldn't have been "polished" given more time because the underlying designs were simply poor. Chapter 3 is basically a ton of boring filler and puzzles ripped straight out of Legend of Zelda games. BG2 doesn't have any systemic issue nearly as deleterious to gameplay as IWD2's broken experience calculation. And while BI/Obsidian have some good writers who did a great job on the dialogues and certain flavor elements, IWD2's story was beyond derpy. NECROPHILIAC DEMON ON ELF RAPE LOLOLOLOLOLOLOLOLOL!
I get that they were rushed. That explains things like bugs, less-than-perfect scripting, some hastily implemented features, etc. But a lot of the flaws can't really be chalked up to that, instead being a result of poor design fundamentals and general mismanagement of resources.