The gunplay and stealth work well, but the exploration feels punishing and tedious.
The story is among the best I've experienced in a FPS. The game does a great job of fleshing out most of your companions via conversations and flashbacks, and it does one hell of a job creating the villains. You know who you hate, why you hate them, and why Jason Brody is willing to go to the end of the world to ensure they die.
The gunplay and stealth come together in a very satisfying manner. If you want to load yourself up in heavy weapons and charge into the base, that's fine. If you'd rather tag your targets from a distance, snipe the easy targets, and then sneak in to finish the rest off via close-range takedowns (instant melee kills), that's fine, too. Anything in between also feels fluid and satisfying. The bare bones stealth mechanics of indicating when an enemy has spotted you does a fine job of helping you out.
The RPG elements where you level your abilities do a fantastic job of making you feel like Jason Brody is transforming into a powerful warrior. You'll find powers allowing you to instantly kill multiple enemies via takedowns, abilities allowing you to move silently while sprinting, health powerups, accuracy upgrades, and more. If you do a few sidequests, you'll have no problem completing the tatau before the final mission in the game.
The bad:
Exploration begins to grow old fast. Do you see that cliff? Well, you're not going to be able to climb up the side of it, so spend several minutes going around. This is especially frustrating when there's just a small steep section you'd like to climb over to reach your objective but you're forced to waste your time going around around. Hell, it's not until the final island in the game you're able to safely descend cliffs rapidly. The time I spent walking around mountains was frustrating when I feel this issue could have been solved with an ability allowing Jason to climb rock walls. In an open world game, exploration should be rewarding, fun, and relatively easy. Far Cry 3 only succeeds in the rewarding aspect by making additional guns, syringes, and pack powerups available for completing side missions and collecting the various objects scattered around.
The exploration is made worse due to inconsistent damage from falling. Sometimes you'll take no damage. Sometimes you'll wipe out most of your health for jumping/falling a short distance or sliding down a cliff.
It's also a good thing there are only 18 towers to reveal the map. These towers require you to climb to the top to remove the signal jammer before the map in an area is revealed. The problem? These towers can be frustrating to climb when Jason doesn't grab a ledge he's supposed to climb or does his feet-first jump forcing you off the side of the tower to his death. Before the halfway point of the game, these towers feel like a chore. Climbing them takes longer than it should, and one misstep sends you back to the beginning. The only reason to do them? Reveal the map to make pathfinding on timed missions significantly easier.
Finally, the automatic save system needs improvement when assaulting an enemy tower or outpost. It usually works well, loading near the tower or outpost you were assaulting before you failed. Occasionally, however, it'll send you to your nearest safehouse, forcing you to trek 300-600m to start the assault again.
All in all, it's a solid shooter. It's unfortunate, however, that Ubisoft failed to make exploration easy and enjoyable.