Trial-and-error is a bad way to play a sneak up game and it ruins the potential of this good looking tactical shooter
The good thing about this game is, that it's very pretty. Graphics are good and scenery is nice. I also compliment the aiming system in elite-level (which is the only level to play this kind of games) since you can't just point and shoot. Naturally the x-ray kill cam is awesome.
But the comes all the bad stuff... The game seems unfinished. There are numerous little bugs and glitches that stick in your eye. Like graphic bugs where your rifle penetrates a solid wall, invisible pixels where you get stuck while crawling... Sound bugs where the "cover noise" suddenly just stops, making stealth kills impossible.
Some of these could be forgiven but it's the actual gameplay that really hits dirt.
First of all, enemy snipers see you INSTANTLY even if you crawl. In the dark. 200m away. Behind foliage.
You'd have to peak out behind a cover half an inch at a time to remain hidden and take a shot. Now I get this if it was broad daylight and I would prance around the battle field. But this dents the reality in a big way. Good thing is that it usually takes max two shots to kill you.
When you combine the fact that the enemy can and will spot you instantly with spawning enemy soldiers, you have a really nice showdown of spray'n pray gameplay. Not to mention that even when firing from a cover 150-200m away, every soldier will automatically know where the shot came from. Others have written about the difficulty of determining bullet ballistics on a battle field and I have to agree. This is silly.
When spotting the enemy sniper, there's a helpful lens flare/scope reflection that blinks the enemy's location...though this can only be seen when looking through your own scope. And it's there in the middle of the night as well. Smooth. But helpful.
The enemy AI doesn't seem to communicate at all. One guard sees a body and starts to huff but the others still walk casually around. Your own shots alarm every guard in the area but a German/Russian sniper can lay down fire without anyone wondering why.
Then of course the age old "special forces elite soldier who can't crawl up stairs or through gaps in rubble and fences, climb through windows or low walls etc.."-bug.
All in all, it's fun to sneak around for a while and get the feel of a true sniper. But all this is quickly flattened by the bugs, glitches, clumsy gameplay and ridiculous AI.