...What's unique? ...What's different? How is this any different than any other game? ...What's DIFFERENT? What's so special? What's so unique that some guy says that this game will be on his harddrive way after everything else fades? What's so compelling that some guy says "best game in years"? ...BUT WHAT IS SO DIFFERENT? ...What's DIFFERENT????
Simple: the experience.
I felt like an actual soldier playing through the SP game, and I feel like an actual soldier playing MP. Contrary to what you seem to think, a game doesn't have to introduce some radical new idea or have totally new weapon ideas to be good. It's one of the best gaming experiences I've had the joy of taking part in, plain and simple.