Most of the criticisms are accurate - the gameplay is repetitive, there's a lot of travel time and there's about ten minutes of story content in the entire 20+ hours of gametime. Voice acting's mostly horrendous as well.
And yet I enjoyed this vastly more than either the first game or its true sequel Crysis. I don't know what it is, to be honest. The core gameplay's fun, but all you ever do is go from place to place carrying out very samey objectives. If you put a little effort into it you can create your own variation - the game is very clearly designed around it. It's why the objectives are so generic. Spend a minute or two with your monocle mapping out an enemy location and planning your assault and suddenly every encounter is far more interesting.
But that doesn't explain how much I like the game. Somehow, after sinking something like 15 hours into it, I'm just enjoying the experience of playing it. Even the travelling is satisfying to me. This wasn't the case at first - but once I got to about the 60% completion mark, unlocked many of the better weapons, and started taking it slower, I'm having fun just cruising around exploring the game world doing everything there is to do.
I don't think it's something you can force, and I don't think it's something that can be summed up properly in reviews. I agree with just about everything in Yahtzee's review from a critical perspective, and yet I wouldn't change a thing in this game.
It's a mystery to me. Doubly strange as I'm a linear, story-driven gamer at heart - Far Cry 2 couldn't be more opposite to my tastes. But once I'd gotten my finger on the pulse of the world I didn't really want to leave it. I went from burning through the story missions in a rush to get the game out of the way, to completing every single near-identical side-mission. To be honest I never understood the people who dropped 50+ hours on games like Oblivion, but now I think I do.
As far as I'm concerned this was the best FPS of 2008.