Hey there! Here's a short "review" of the two missions in the campaign:
The first cutscene-mission where you get to go inside and blow yourself up, incidentally, was a very nice little piece of interactive storytelling: well done! I also liked the whole experience, very cinematic. You need voices, but what mission doesn't?
Devil's Castle was all right, but as Gotcha said, it's...a little unbalanced. You like your forest fights I see, and no problem there: I also think the AI does its best in forests and makes things the most interesting, BUT: the damned "this person can't die" thing! Also, why so many Chedaki?
How about you add a lot of Chedaki moving in through the forest towards the castle, as they surely heard the shots and are heading there to investigate. That way the clever player can attempt to sneak past these groups without engaging them, and then just fighting his way through the remainder. What I did to finish this mission ultimately is the same I do whenever I can: I went around. Didn't fire a single shot, which might have been what you intended of course, but still.
Also, at the very end I watched a Chedaki through my gunsight, standing at the edge of the forest with his back towards me, through the whole chopper extraction
Basically, they don't react in any way to the big, loud helicopter arriving on the scene, which is a little unfortunate. How about you make it a Hind instead, add some kind of information-sharing script (so that the player can "spot" targets for it) and then let it rip lose on any Chedaki wandering too close to the forest's edge? It could also engage the reported armor targets (or maybe a secondary helicopter could do this): this would add a bit of boom-wham-explosion prettiness to the mission as well.
Finally, I suggest adding the first aid module to the lieutenant (you can add it just to him in the beginning - he will still have it when he joins your group). I also suggest you do this to Olegich in mission 2.
As to mission 2: Good cutscenes, speaking, plot, etc...all fine and well. But the god-damned running-after-idiot-AI thing! No! Just no! I got stuck at one particular spot trying to keep Olegich alive restart after restart: all he does is get himself killed. And no wonder: we're two guys against a whole forest of Chedaki! Why doesn't Olegich realize the situation is out of hand and try to turn back, run away, DO something? Even if he'd just lie down and tell you to handle the bad guys, anything...but no. So this, I'm afraid, is not gameplay-wise a very nice mission. If you don't feel like changing anything else, at least add the first aid module to Olegich: that will hopefully give him a longer lifespan. Also, make the first "scout" unit you encounter a sniper instead of the one up on the hill, that way the player will be about 100% more effective when the shooting starts thanks to the Dragunov.
I'm wondering: have you changed the cfgprecision in your config for enemies (like many people tend to do)? Or are you using something like ACE to make and playtest the missions? Since these are not simple situations or easy, "start of the campaign" fights you put the player up against here, IMHO. The storyline, the characters, and the basic setup of the missions is great, but for now the frustration > enjoyment, at least in the second mission.
Keep up the good work though, I hope to see some more of this campaign!