Great game with some annoying flaws.
Good:
The weapons in this game are fantastic. There is a wide variety of weapons, about 40-50 total, plus some with custom modifications You will have a ton of fun collecting new weapons. Also each weapons has about 3 different ammo types. Many weapons will share the same ammo, for example all variants of the AK-47 use the same ammo. Also you have a combat knife which is great for stealth kills from the rear.
Good: Combat. Outside of the occasional AI bugs, the combat is generally very fun. Its somewhat similar to a game like GRAW where the emphasis is on realism. Sorry, no bunny hopping allowed. You will have to use cover effectively and make every shot count. Stealth is also very useful in some situations. Head shots are your best bet especially mid-way through the game because enemies will start wearing body armor.
In combat each weapon handles distinctly and you can zoom in with the right mouse to use the iron sights or a scope for better aiming. The weapons handling is very realistic and unforgiving. For example an AK-47 has a huge recoil just like in real life and you wont be able to keep the gun straight during full auto. More advanced guns like the G-37 handle much better. Overall, the shooting feels great if you are into realism.
Good:
Open-ended gameplay. In general you will be rewarded for exploration and thinking creatively. You can pretty much go where you want and kill who you want. There will be consequences for your actions, so dont expect to freely go on a killing spree in a town. One fun and creative way to get some free guns is to roll an exploding barrel near some neutral NPCs. Shoot the barrel and you'll kill them without turning them hostile, then loot their bodies for free ammo and guns! This is just one example of how you can use unconventional tactics to progress through the game.
Mixed feelings:
HOWEVER, if you dont like open-ended gameplay you should probably avoid this game. Its very easy to get lost especially with the confusing map system. You will also spend quite a bit of time jogging from one location to the other, which can be boring compared to the non stop action of a traditional FPS like Half-Life
Mixed feelings:
The AI. Great in some places, horrible in other places. In a fire fight most of the time the AI is very smart. Dont expect them to charge you. Enemies will work as a team, use cover and flank your position. However sometimes the AI will "shut off", meaning the enemies will stop fighting and just look at the sky or the ground. Thankfully this bug is pretty rare.
Mixed feelings:
The Graphics are atmospheric with good lighting, good detail, yet somewhat dated and grainy looking textures. You will need a good system to run the game at high settings. I recommend a minimum Nvidia 7800 or ATi 1800.
Bad:
Lots of bugs. Im playing version 1.003 and whatever people tell you let me assure you this game is still buggy as hell. Some quest cannot be completed if you do things in the wrong order. The game can hang a bit after entering a new level. Rarely, maybe once every 7-8 hours or so, the game will just freeze. Also there are AI bugs as noted above. Thankfully the game is still being supported and a new patch is weeks away, or so I hear.
Bad:
Cumbersome inventory system. Once you start getting a lot of items things get really cluttered and annoying. Your best bet is to pick two stashes to hold your items; one for large items like guns, the other for small items like ammo and healing. This will make organizing things MUCH easier because you will not have to scroll through your guns before the other items. Trust me on this you will thank me later.
Overall:
I really like this game and its definitely a very special experience that I wont soon forget. However it does have its share of flaws and annoyances. Mainly the bugs and annoying interface/item management are what bring this game down a notch. Its not for everyone, especially more casual gamers that dont enjoy open-ended gameplay. If you can handle the occasional bug and you're not afraid of a little freedom, you'll find yourself deeply immersed in a unique and overall very enjoyable game.