Most of the things you were liking in the beginning part of the review are in the original as well, as I found out when I rented the first recently... and beat it rather quickly.

There were plenty of achievements to be had however, so I can see for someone with Live GOLD and enjoyed the game immensely would enjoy it.

Myself, I enjoyed Army of Two a bit more, though they were very similar as far as a co-op experience, though Army of Two had much more variety in strategy.