Strangely enough, I enjoy the sniper levels as a break from the mad grenade rushes of the other maps. I find that I do better on those maps if I run around with the pistol. Then as soon as I see an enemy in the distance, I dive to a prone position, switch to rifle and plug them. You can do the whole maneuver pretty quickly.

Regarding Stalker - there will be multiplayer. The standard deathmatch/teamdeathmatch, coop, and interestingly - Human -v- Mutant.

The solo play is a free-form FPS role playing game. Basically think of Fallout, and you'll get the picture. You can run anywhere and do whatever you want. There will be mini-quests, etc, as well as the main quest.