The space marines with grenade launchers either need a nerf or they need to never spawn in the same room with each other. I've run into pairs of them twice and both times I went straight from no deaths to failing the mission. I consider everything else in the game way too easy for the record. But when you have two grenade launcher marines in the same place it's basically an automatic death because they take turns shooting you and you're crowd controlled almost 100% of the time. You can't fight them and you can't run away.