Pretty much this + shit rewards. The timer really just MURDERED any potential fun. I get what they were going for but they should have realized how basically un-fun the whole thing was. You can't explore, you can't look around, you can't understand the encounters or the quests, you can't appreciate the atmosphere, because Blizzard have designed it so unless you're in maximum GOGOGOGOGOGOGOGOGOGOGO mode, even on the easier settings, you could lose. It made the BGs look chill and relaxed for god's sake. A ghastly mistake, frankly.
Add to that the totally rubbish rewards, which they never really fixed, and the fact that you absolutely HAD to have three people, no more, no less and it was just... ugh.
Sad because I love the concept and I found the AI enemies quite amusing and engaging (hopefully they can find uses for that tech in SL), but just no to GOGOGOGOGOGO content.