Same here. The game was good before 4.0, it's not fun anymore especially when you need to upgrade new weapons. 
I tried and failed numerous times to finish a mission in ruthless, it's impossible for me to complete them alone, while I was able to finish them most of the time prior to 4.0.

At first, it was a real pleasure to dive into a game where you could have a blast mowing down hordes of Tyranids and crushing Chaos troops, all while experimenting with the different classes. So much fun to crush them with the assault...  

But guys from Focus, there's not a lot of content in your game, some missions are too long and just painful to repeat (I mostly play missions 1 to 3). 
There's no feeling of being a Space Marine jumping into the enemies and crushing them, now it's like a survival game (is it the new concept? ;p).

The mechanism of weapons upgrade is a punishment, especially when you've already leveled up your class, it's too damn long!!!!!!!.
Some enemies are just bullet sponges, I'm just continuously unloading some of my weapons on them, even if I upgrade it, we should feel like we're shredding them to pieces.

It seems to me (but I may be wrong) that you rely in this twisted way of developing game: balance between frustration and reward, which is a toxic and lazy way to design a game.
Instead you should have focus on content, good stories, different kind of operations/missions, some short, some long, some for 3 players some for more.
Maybe you were surprised by the success of this game, unprepared. 
After all I would say it's a shame because the universe is great, some of the maps are awesome, the different classes are fun.
You had all to create a fantastic game with a large community in my opinion.

But today, you are lucky that the selection of games is very poor right now.

I'm sorry, I know I'm hard on you, because maybe I hope that it will wake you up and you would prove me wrong.