I'm finding it impossible to deal with Far Cry 3 in its own terms. It's much easier for me to talk about it in terms of games it's not.
It's not Far Cry 2, for example. Oh my God, Far Cry 2 hates the player. Never mind the respawning enemies making sure that every square inch of that game's sprawling African savannah was actively hostile towards the player. And this was the least of your worries. More than once when I was playing that game, I found myself in the middle of a firefight when my gun would suddenly just fall apart in my hands (weapons 'wear out' in Far Cry 2), I'd panic and run away to consider my next move and that's when my character would suffer a malaria attack (your character is infected with malaria at the start of Far Cry 2 and spends the rest of the game dealing with this). And then I'd die.
Far Cry 3 is not this. It's much more forgiving. More hand-holding. Almost to a fault. Straying too far off the prescribed path (even during the tutorial) will result in a 'mission failed' screen. It's not messing around. It doesn't want you actually exploring the huge, open island without making sure you fully understand the mechanics and the context. As helpful and friendly as this is, I can't help but feel like this is a step back. It takes fewer risks. It's less dangerous. Much as I disliked the random bullshit in the previous Far Cry game, it was at least remarkable.
Speaking of exploring, Far Cry 3 is not Proteus or Misasmata. It's not even Dear Esther. These are all island-based games that are very much about exploration. Proteus and Dear Esther are nothing but exploration. You get from it what you get. Miasmata has a story and a history for you to peel back, layer after layer. Your exploration is rewarded with a deeper understanding of the narrative. It's like the designers took a look at Lost and thought "there's a game there."
Far Cry 3 is not that either. The game is set on a couple of huge, open islands with a long, varied history, but there's actually very little to explore. Every hut on the island is the same. Every cave is the same. There are WWII-era gun emplacements. There are downed aircrafts. There are beached tankers. But these are all just eye-candy, not actually things that affect your game in any way. They don't reveal anything about the story of Far Cry 3 or the history of the Rook Islands. I found one cabin with a body in a noose, but without any context for who this guy was or why he hung himself, it's just a meaningless non-sequitur.
And this is the problem with Far Cry 3 - it's an enjoyable romp, but it doesn't have any aspirations to be anything new or original or even different. The entire plot is built on a series of tired Alice in Wonderland parallels (with a healthy dose of references to The Beach thrown in for good measure). And it could easily have been so much more. As well as his arsenal of heavy weapons, your character is also armed with a camera -- a tool for exploration, for documenting things -- and this could have been used in interesting ways; integrated into the gameplay somehow, but instead it's only ever used to identify enemies before you kill them.
As much as I'm enjoying Far Cry 3, I can't help thinking of it in terms of games it's not because it's just a very bland game done very well. And it could have been so much more, if it tried.