I will agree with most critics that its a decent game but I found alot of flaws with the game mechanics, characters and the storyline.
Here are the things I found to be mediocre.
1) the game is too linear. Its impossible to fall while climbing. You just press up and "Monkey" climbs automatically to the top of the tower. You can't fall off the edge of any platform. Invisible walls are all over the place.
2) More than half the upgrades are useless. Besides Focus Attack the rest is useless trash.
3) Once you upgrade your life regen, you are nearly immortal and health packs serve no more purpose.
4) The bosses are boring and are more platformers than actual combat. The way to beat the final boss is to climb towers.
5)The world is one giant recycled jungle. 70% of the game looks the same.
6)Its a really really short game!
7) The collectables and secrets are utterly useless. Just a bunch of flashbacks giving you nothing at all...
8) The story is basically a cheap rip-off of the matrix.
9) Enemies are easy. You can just attack stun them attack stun them use Focus Attack Bam! everyone is dead! There is little combat challenge if at all... I died maybe twice the whole playthrough and this was mostly due to getting stuck in some corner and suprised by a mech from behind.
10) The stages are repetitive and boring. Even the Trip / Monkey puzzles are really simple and uninteresting. Its nowhere near as good as ICO and the climbing is just moving up since you can't really fall.
11) Once you get all life upgrades the end of the game is easier than the beginning. Your health regens all the time and so does your shield. The end of the game pretty much showers you with Ammunition meaning that you don't have to even approach your enemies to kill them. You can just Shoot at them since the Ammo is everywhere.. same with the final boss..