Finished the campaign today. Something crazy above 40 hours. Though I did grind a bit in act 2 to get a certain trophy, and again in the final act because I felt I needed it to beat a boss (and I was wrong!).
Speaking of which, the final act is total bullshit. Sorry, but fighting these fights is just stalemate central, nothing ever happens. 10 minutes is a good length for a single "battle", and for most of the campaign, that's what you get. Enter last act, and you might be looking at 30 minutes, or even 45 minutes of back and forth, nobody doing anything but piddly damage. Or none. Because mana shield.
It's the units. Gremlins suck the fun out of the game because they are totally overpowered defensively as soon as they charge, they nuke opposing chargers easily, but they just don't deal damage to the hero. So stuff keeps crumbling and exploding all around, but the heroes live forever. Djinns literally freezing entire columns doesn't particularly help the pace either. And to top it off, the special wall ability there makes all walls crazy strong, on both sides. So there's even less chances to deal hero damage.
That whole act really was a chore and left a bad aftertaste. Which is a goddamn shame because everything before that was brilliant, fast paced and fun.