So, let me preface this, that I know this is an alpha. It's no where near complete, and the purpose of the alpha is for those of us who do the Founding, to be able to give feedback, and improve the game as it develops. With that said, I can't give feedback, if I can't progress.
I have tried on about 4 separate occasions to do a mission in game. Three of those times, the game locks up, gun fire/combat sounds in an endless loop as the game quits responding. Two of them were full screen, unfortunately on my primary screen on a dual monitor set up which required a reboot to address. The third was borderless windowed, where I was able to force the game to close when it locked up.
The fourth time, where the game didn't lock up? Was on a purge mission with the Heavy crusader that I had to quit, because I was literally unable to complete the mission. Why? Because the Heavy crusader, to my knowledge, has no way to get the chaos portals out of the healing mist, and can't experiment with doing this because of a problem I noticed in Van Helsing, which got me to quit playing that game, and telling people to look at other ARPGs.
Constant enemy spawning to the point that you are overwhelmed, is not difficulty. It never will be difficulty. It is obnoxiousness that takes away from the enjoyment of a game. When I cannot figure out how to complete a mission, or how the character is supposed to complete an objective, because being near the point that I can't do anything to is constantly spawning enemies who never cease coming? That isn't challenge. That is frustration to the point of saying "Forget this game."
if the answer to the chaos portal thing is "play with x class that can knock it back" then that is a profound error from the design aspect from the ground up. I have no problem playing games with friends. I have a problem when the game punishes you for playing solo, or not playing the correct class. And make no mistake, this is punishing you, because it is time that is literally wasted, on missions that you can't complete.
tl;dr The game is locking up and crashing 75% of the time, and the other 25% the game has unwinnable objectives. I can't give feedback on progression much less any other mission, because, through game crashes and game design, this is not available to me.