I was just wondering that myself the other day! It was an outstanding title and deserved some recognition. Maybe it just came out too early in the year. Whatever the reason it's a shame. But we know better!
Because, while it was one of the few western based military-esque games with an actual plot and interesting story-telling device, it was overshadowed by the annoying guards and the fact that spies vs mercs wasn't included in the game.
I loved it though. Too short for my own taste though.
While a great game, I think it just didn't have that "Wow" factor. You know that thing that you remember 8 months later. While it innovated the stealth genre with its Jason Bourne approach to action, while maintaining some stealth mechanics it didn't have that really memorable thing that sets it above other games.