More feedback it is, then! Last time I threw out some more general concepts about bosses in general. This time, I'm going to try to focus on giving my full thoughts on specific bosses.
As the first boss, his introductory role feels very evident when leveled up. He seems slow, and with enough player damage, he doesn't even get a chance to summon skeletons. Having some other monsters there from the start gives additional sources of damage and presents a situation to assess. The attacks that he "tells" might feel fresh and more challenging if a series of them happened in quick succession. For example, he has a tell where a blur of him moves toward the player and then teleports to him to attack. Doing several of these in a row on higher difficulties would be an interesting surprise. Perhaps even making the number of times in succession could be randomized so the player can't get used to how many there will be.
The feature that's supposed to define this boss, according to quest characters, is devouring victims. Aside from acid spew, I don't get the feeling that this thing is about to eat me. I don't feel a strong need to get out of the slowing web, but if too much time there meant being wrapped in a cocoon and drained of blood, restoring life to the boss, I might rethink that. It might feel similar to Diablo trapping the player in a cage and then sucking some life out, but that would be a good thing to steal from.
I get the feeling this isn't meant to be a proper boss, and merely a unique quest monster. I'm not sure if this is intentional or not. If so, I suppose he'll have to do, but if not, he would need an enormous overhaul. I never feel like his molten affix is meaningful, because there's no way he's going to get around me. I think it would be more interesting if he laid a stream of fire in the lane I was in. Other possible ideas would be to have him apply chains that do progressively more damage to the player over time. There are a few directions I see possible, either a) having the chains break by distance, or b) More chains are applied as the fight goes on, which gradually reduce the player's speed, and limit the distance you can be from him.
This fight is very polished, so it's hard to really recommend adding anything mechanically. It might be an interesting homage to have him behave more like his Diablo classic counterpart once he gets down to a certain level of health, losing the sickle to instead move directly to the player and attack quickly, also using his charge attack more frequently to keep it from being to monotonous and unfair.
As a Wizard primarily, I've heard "no more illusions" so many times that I'm surprised she doesn't do any illusion tricks in this fight. Perhaps she could have illusions, starting with one at the beginning of the fight, and adding more whenever she comes out of invulnerability. A completely different idea would be to mix things up by making the last pack of minions invulnerable instead of her. At the least, I feel she needs one more "phase" to become interesting.
I'm rather happy with this boss fight mechanically, aside from the fact that rocks falling from above are very hard to read (as in, tell where they're falling). I generally see this fight as "stay out of that one small area" whether it's the Slow Time bubble or the falling rocks (usually both together). Once we can better tell where the rocks are going to drop, I think it would be a nice mix-up for there occasionally to be one small safe area to gun for instead, with the rest of the chamber collapsing around you. It would certainly go a long way for bumping up the scale of the fight.
The overall fight with Belial is quite grand, but the mechanics of the earlier phases are much less inspiring. For example, the three "insect missiles" seem like something to be dodged, but the space doesn't afford that well, especially if you're pounding him in the face. It would be interesting if he imitated the Witch Doctor's Plague Bats skill sometimes when close to the player.
How could we make Ghom more disgusting? Should he reconsume his monster boogers for life regeneration? Vomit exploding corpses from his terrifying belly-mouth (after some hacking noises that warn the player, of course)? Those seem pretty vile to me.
The best I could come up with for improving this boss would be to make the landscape more interesting. I really like this boss as a hulking wrecking ball, but I feel it would be a bit more interesting if there was some degree of chase involved. Much like Demonic Tremors break through doorways, the Siegebreaker would have to be led to break things that would topple on him and weaken or damage him.
Even adding something like a charm spell to Cydaea's arsenal would make her marginally more interesting and actually seem like a Maiden of Lust. While scooting back after webbing the player makes her smarter than Aranae, it doesn't match up with Cydaea being the image of Cydaea as a demonic temptress luring you into her traps that other NPCs make her out to be. Whenever she runs across the room, I feel she should leave some sort of devastating trap, so there's a more compelling consideration at hand concerning chasing her. Particularly if the player knows he might be charmed, and getting even close to such a trap may be inviting disaster.
Like Zoltun Kulle's falling rocks, Azmodan's Meteor seems a bit hard to read where and how close to the ground it is. I am a bit surprised that he never thinks to summon more than one gate for minions at a time. Perhaps he will also learn to call on something more than just demon troopers, too.
He may not be a particularly deep boss, but he's adequately terrifying. I feel like trying to change him might take away from that. So, no suggestions for him.
Most of Rakanoth's feeling of despair is tied up in doing lots of damage seemingly out of nowhere. For being an alegorical overcoming of Despair with hope, I feel like Auriel seems too uninvolved. I imagine Auriel helping, perhaps by providing "seeds of hope" that the player must collect to gain a buff. Without this "Hope buff" players are unable to damage Rakanoth.
Frozen affix and ... that's really it. It works for normal, but after that, his uniqueness is lost. Guaranteed freezes work well as transitions, and yet there isn't much of a transition. Perhaps after the first freeze transition, Izual gains the ability to use his own version of blizzard, with blackened ice pelts to distinguish it from Wizard players' blizzard. After the second freeze transition, there is also a chilling mist covering the entire area (or alternatively, covering various portions of the field that shift through the remainder of the battle).
Easily the most layered and grand fight in the game. Diablo does so many interesting things that you can't really add more to the fight. The shadow clones, however, have started to feel like a rather insignificant part of the Realm of Terror phase. I feel that the clones would be better if they focused on using class abilities that were interesting to avoid - examples being the Barbarian's earthquake, Demon Hunter Traps, Wizard Twisters, Monk's Sweeping Wind, and Witch Doctor's grasp of the dead. Otherwise, the experience feels like brawling a weaker version of yourself that doesn't last long enough to be interesting.