Oh yeah act 3 is still a great game. It just lacks the polish and consistency of the first two. I'd still really enjoy it if the full game was of the same quality as act 3, it's just that they set the bar very high with the first two and the last one doesn't quite hit that mark. It has some of the best parts of the game in my opinion:
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House of Hope and Astarion's questline spring to mind
They've also already fixed a lot of things, to an extent that you rarely see in the industry:
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Such as the Karlach questline, where they even called the VA in to record new lines and whatnot, just a few weeks after the release
and with their track record with definitive editions (both DOS1 and 2 got massive updates), I can't wait to see how it all turns out.