It's interesting to see such varied opinions.
My pick is easily act1>3>2. Or maybe 3>1>2.
Frankly, I think all of the acts work better by themselves, they just don't glue together into a coherent whole. I didn't like act2 because it disappointed regarding what act1 set up, and didn't contribute much to the story going forward. I probably enjoyed act3 the most in some regard - single, packed with content map finally felt alright here - but I found it difficult to not be annoyed how plot threads from previous act get sideline, abandoned or retconed. At the same time, narrative stuff is troubled throughout the game, so it is difficult for me to put blame on one chapter over the other.
Still act1 is polished to the point, that I was able to overlook a lot of game's flaws and really engage with the title. Later acts have very much disconnect that I had with early access.
Act2 is the only one which I found boring. From the inconsequencial shadowcurse, to most of the act focusing on uninteractive backstory to an underwhelming, boring and uninteractive villain, who becomes irrelevant as soon as the act ends. Aside from gith creche and finale, the act could be cut as far as I am concerned.
