It is not, to the point i played there are 5 kinds of enemies:

1. melee gaunts - rely on numbers and running around and strafing to confuse the hell out of you what is even happening around you
2. ranged gaunts - rely on being small not very visible and shoots you from some distance
3. tyranid warriors - rely on being hard as fuck and forcing twitch manual fingerbreak every few seconds, also on numbers, even on easy there are many of them.
4. ranged warriors but they are easier than gaunts since you can see them better, they also just kinda stand in one place
5. zoanthropes, absolutely miserable shit 10 times harder than they should be and bombarding you non stop with very hard to avoid fire which also staggers you all the time

Oh there was also Carnifex at one point but it was easier to fight than the warriors, but scripted so you couldn't defeat it.

I must admit all of those maybe except ranged warriors are very effective against my old and somewhat damaged nervous system.

It looks really cool visually but I can definitely see it getting old without variety. Gears of War kinda understood this, or at least some of those games did. I sort of see Space Marine as similar in style.