I'm currently in Act 5 now, which I think is the final Act. I feel like I'm flying through it and the game really doesn't feel so hard, I'm even playing it on hardcore which is what I hear is recommended. There are some tricky parts but its nothing too taxing that a second try won't get you through it. Also I find the friendly AI to play a bit wonky a lot. They have more health than you do and they will often just run the fuck up to the enemy to where sometimes it will just be a jumble of your COG teammates and locusts or lambent just running around each other meleeing like crazy, it can be a bit ridiculous at times. I also tend to fall down a lot more than they do. Most of the time they revive me but I've had some few occasions where there will be a COG really close to me and they do nothing. So yea, the friendly AI is my biggest complaint about the game so far, but seeing as how this is a trade off to deal with for 4 player coop, I'll take it.