It's been patched op. When I played it at launch act 3 was like a frickin bethesda game
Had to turn pc settings down because it had way worse performance than act 1 and 2 which both looked great and ran very smooth. It runs well now after the patch except when I activate ithillid powers, prepare to throw an item during battle (yes I'm carrying a lot of stuff) or separate my party by a long distance, these things cause issues. Act 3 must be just awful on console, if I had to guess.
Act 3 was filled with fun killing bugs in the first month. I blew up a prison but would still see video footage of people trapped in the exploded prison in the steelworks foundry. Then when I rescued a guy from the foundry, I was walking around looting with him standing there, and he stopped me and made me pass an ability check for tresspassing. The guy I was rescuing stopped me for tresspassing in the place he was imprisoned halfway through me rescuing him from it! My shovel stopped working and I needed 2 shovels to dig up chests, my wizard found a cool staff with a glowing light on the end but the light would just glow in the wrong place away from the staff floating in the air. There was a haunted painting quest that just glitched out and the people wouldn't talk to me. There were lots of weird conversations that, based on how glitchy everything else was, I felt lines or scenes were missing from.
During the ending cutscene, there is shot of people standing outside a building called sorcerous sundries. The building didn't even have textures in this cutscene. Not low res textures - NO textures. I took a screencap if u don't believe me. Useful abilities I get from equipment would just stop working in act 3. I would look through all the menus during battle and couldn't find them, the only way to get the ability back is to wait until after the battle, unequip the gear and reequip it. The doomlobber gloves is one such example, it lets you cast spells in melee without penalty but it stopped working in an important battle.
That problem is still there after the patch actually, although I think it happens less often. During my second playthrough on tactician, my thief had clothing that bestows the "cat's grace" ability and it wasn't working in act 3 until he unequipped and reequipped it. There are other problems post patch as well. I rescued prisoners and blew up that prison again, and the foundry now no longer shows footage of prisoners trapped in a facility that doesn't exist anymore. But, during the rescue I clicked on a security camera showing footage of the prisoner's cells after busting them out, and it show doubles of the prisoners. One still trapped in their cell, and another standing front of the cell as they headed towards the exit. After completing the whole daring escape and thinking I'll just climb out of the escape boat and then quicksave, the game crashed with a black screen as I was climbing out and I had to do the whole mission again, which didn't happen on my first playthrough. When I slayed a dragon and picked up a magic helmet the dialogue for picking it up played twice, then when I warped to camp and I talked to character about it there, their dialogue played twice as well. I got a kickass magic trident in act 3 that magically comes back to your hands when you throw it - it's in the item description. Or it did, on my first playthrough. Now it no longer consistently works, and I have to find the trident after throwing or load the game when it disappears. None of these flaws are enough to ruin an amazing game, but they are still noteworthy problems.
Act 3 does a great job with story and quests. Personally I think Ketheric is much more interesting than Gortash and Orin combined, but there are good story payoffs for companions and callbacks to things that happened way back in act 1 in act 3. Even if you screwed up a quest in act 1 it can sort of partially payoff in act 3. Like there was a lady whose husband I was meant to rescue but instead he died screwing up the quest. But I was able to meet a cat in act 3 and convince it to bring companionship to the widowed lady. That's really impressive attention to detail. However if you like gameplay more than story there's a very bad kill to talk ratio in act 3. When I'd like to fight a series of battles followed by an interesting conversation I'm more likely more likely to get stuck in a series of conversations and finally a battle afterwards. You also spend more than half the act at max level with no level ups to look forward to which is a bummer.
TL,DR: Act 3 is great now after the patch, but it is still the buggiest of the 3 acts. And the weakest overall in my opinion. But I don't think a player would feel this way if they were playing primarily for story.
That wasn't the point.
