But causal fans or even hardcore fans see Prometheans and aren't intrigued by their existence or their relation to the Forerunners, really I think thats one of the main issues with gameplay motivation with the Prometheans in the fact that you see them as a simple mindless pawn ( a similar thing has now happened with the Covenant.)
One thing that made me dislike (and not hate) the Prometheans is that I never understood why they were fighting me (Master Chief).
Personally, I did liked the Prometheans during the first part of Halo 4, when they were blue. They didn't really attack us since they weren't making a difference between you and the Covenant. They were just protecting something, like the Sentinels in Halo CE/2/3, and that makes them intriguing to me.
But after that, they fall flat, and while the Covenant had a religious motivation to wipe me out, Prometheans during the second part of Halo 4 and during Halo 5 had no real motivation to fight against us, they were just robots manipulated by someone.
And I'm not even talking about the bullet-sponge side ofc. Scott Warner gave a really interesting talk at GDC regarding "The design of new ennemies for Halo 4". It's a one hour talk and it gives us an inside look at how they were designed, from a lore and gameplay standpoint. The first iteration for the Prometheans looked like really fun to play against, I don't really know why they changed the way they were behaving, maybe because they wanted to give player a harder time, making Prometheans more challenging, even if they ended up being more bullet-spongee than anything else.
If you're curious about this talk: GDC 2013: Scott Warner - "The Design of New Enemies for Halo 4"