"Frontlines" level was a real pain in the ass level for me. It's hard to find a stealth route in pitch-black darkness (and yes I've maxed out gamma), so I opted out for trial-and-error and I find this approach cheap. But once I passed communists it had become much easier. Actually I passed fascists tunnels without dying, once I got grasp of stealth mechanic. You can come really close to soldiers in crouch mode - they don't hear you. They can see you though, so the closer you get to them, the safer you are (at least in my experience).
And the "turret section" was just wow. Same goes with the next level. The game has become scarier, that's promissing.
Now it's time to fight inertia. People who've beaten the game know what I mean
I really hope it'll sell well, so they can fix some of their design decisions. The game has the potential, especially in stealth part, but they need to make rules more consistent and clear to a player.