It's a good game with few flaws, but doesn't amaze either.
Controls - For the most part (see below) the controls are easy to manage, and provide the kind of response you need. Aiming is good, context sensitive actions are used well, and you can manage tight spaces fairly easily.
Weapons - You get a decent selection of weapons to use in the field, but aren't overwhelmed by the available options either. You also don't find yourself wishing you took the other gun, because there's no ammo around for the one you picked up.
Game-play: There's a mix of stealth and fire-fights, but be aware that I personally found there was a greater emphasis on the fire-fights. It could be that I am simply no good at being stealthy. It's also one of the few games where the escort missions were not a huge irritant. The people that you need to escort move when you tell them to move, and take cover when you tell them to take cover. They also did the latter effectively, as opposed to just stopping in their tracks and ducking. The AI was also kind enough to focus most of their attention on you when you start shooting at them.
Mission length - Considering it's a PSP port, it has an exceptional campaign length. It took me as long to play this game as it did some other made-for-PS2 games.
Gadgets - Standard equipment is included, but the fact that it's common equipment doesn't make it any less fun to use. There are 3 goggle modes: heat vision, IR, and a 3rd mode to detect important items and electronic signatures. An "RTL" is also at your disposal which allows you to zip line along overhead wires.
Unlockables - There's bonus items (like new weapons and levels) to unlock by completing various tasks throughout missions, and by collecting "evidence files" throughout the levels. If you're a completionist, there will be lots for you to do that will encourage another play-through.
Locations- There's both outdoor and indoor levels ranging from snowy to sunny locations. The level maps are also laid out well. They feel large, but not confusing.
WHAT COULD HAVE BEEN BETTER:
Controls - I did say that overall the controls worked very well, but there are a couple of items that could have used improvement. I found the inventory system and the way you switch weapons to have a higher learning curve than needed. Once you got the hang of it, it was fine, but it could have been updated to better utilize the PS2 controller (as this is a port from the PSP system). The other thing was that it was sometimes frustrating to get you to lean up against the walls. This move (completed by pressing the analog stick twice in the diretion of the wall you're standing near) allows you to peak and shoot around corners. It's a great feature to have, but sometimes the game didn't realize that that's what you were trying to do. So occasionally you'll find yourself just walking into walls for a few seconds. This could have been a easy fix by doing something like mapping the move to the L3 button, instead of having to double tap forward.
Repetitive missions - The core game-play itself is fun, and I'm not saying that the game is boring. It's just that the levels didn't seem to deviate from the core game-play very much. The majority of the levels were mostly just creep and kill, creep and kill, creep and kill with a few very simple switch puzzles here and there. This was another minor concern for me, but again it may be a larger issue for other players.
Linear style - It's not 100% linear, but there's more set paths then there are multiple ways to complete your missions. This didn't both me at all, but for those that like a more flexible and robust set of missions may be disappointed.
If you like the whole stealthy operative style of game-play, then you'll likely have fun with this one too. If you're new to the genre, you may have more fun than someone else. If you're a veteran, I don't think you'll find a lot of innovation here.