I'm finding this game to be way to hard. I can't get past the first mission. Can't image how hard the other missions are. When is an easy mode going to be added for us casual gamers?
Are you sure you are not playing on hardcore mode? (Hardcore mode you die in 1 shot).
Also all the missions should be unlocked in the alpha version, so give a few others a shot.
For the first mission just take it slow and make sure you blow up each of the shacks with a grenade (Or shoot barrels).