The main problem I see with Nemesis is that the script needed a lot more work, and the director was so far up his own ass he didn't realise he wasn't the great visionary he thought he was.
Nemesis really could have been a great movie, but it just didn't hit the marks it needed too. Most of the problems could have been fixed at the script stage, and it's a real pity they didn't see the problems at the time.
Now that said, I don't think it's the train wreck many people do. And I still maintain that if you went back to all the raw footage you could cut together a much better movie than we got.
That said, it's still a bit of a guilty pleasure movie for me. I was pretty disappointed with it when I saw it, but for all it's flaws, I don't mind it too much these days.