As most have said, as a stand alone game I think it is superb. But I think there are a few things that put people off about it:
3. It's a hard game. Best for those who like a bit more of a challenge
2. It's not based on a world that contains every environment on earth (snow, larva, desert, inside of your nicotine addicted auntie's lungs etc.)
1. Comparing it to MP1. It just shouldn't be done. There are so many differences.
Must admit though that I thought the weapons and visors from MP2 needed a bit more umph. Dark visor was a rip off of the heat visor and the Echo visor wasn't used enough or in many different ways. Loved the look of the Echo visor though. Need I say much about the weapons? But all these things aside I did really enjoy this game,