The problem with the Prometheans is that they break certain “Do not do this” rules when it comes to enemy behaviour in First Person Shooters on Consoles. It’s a known concept that it’s not fun to shoot enemies in FPS games on consoles who are either very fast moving, or they’re hard to hit, or they’re bullet sponges, or they come back from the dead after killing them (or nearly killing them).
As enemies, the covenant did not really have these issues. Each enemy in the Covenant faction could be killed by shooting them outright, but they also had unique ways of defeating them whether it was using the plasma pistol to pop shields, flanking behind them to shoot them in their back, dodging them as they rage charged you, counter sniping, etc.This kept the engagements unique, fresh and fun.
Granted, I recognize that there are only so many ways to create to defeat an enemy in an FPS.
However, with the Prometheans, despite that some weapons may damage them more, the entire pattern of killing them is keeping your crosshairs on them and unloading bullets. Even the Knights who have specific weak points to target, can still be killed by unfocused brute force. This is not fun because it boils down not to unique ways of defeating them, but just to keeping track on them and firing.
It becomes even more frustrating because they have been specifically created to be fast moving and dodge sporadically in a 3D space. Covenant troops dodge bullets and grenades as well but its usually to the left or right and typically as a reaction to what the player is doing (shooting, or throwing a grenade). You can anticipate this dodge and counter it.
Crawlers, Watchers, Soldiers can dodge on all axis plains (X, Y, Z) at a moments notice and it’s not usually in response to player action which is frustrating. You may be shooting at a soldier and they will teleport away (sometimes multiple times in a row), forcing you to reset your aim and continue firing. They easily nullify any and all strategy using their teleporting ability. If you have the high ground, they’ll appear behind you. Combine that with their bullet-spongeness and long time to kill and it results in a frustrating gameplay experience. It’s a sign of bad enemy gameplay design.
The same goes with crawlers which will swarm and kill you no matter where you’re hiding, while they move in random directions with small hitboxes so they’re difficult to hit/kill. Granted, it’s easy to take them out with a rifle, but using any other weapon calls for unloading shots while they overrun you. Again, bad enemy gameplay design.
Lastly, Watchers are frustrating because they will just fly away at the sign of damage but return to complicate matters when you fight other enemies by regenerating their health, reviving them, or providing shields. So not only are they hard to hit, but they undo any progress you accomplish unless you take them out first, all the while soldiers, crawlers and knights are trying to take you out. The engineers in ODST performed better as a support character as buffed enemy troops but still had a fun experience in trying to kill them.
TL;DR: Instead of developing enemies which have unique ways of being taken out, the Prometheans were developed to force the player to unload lots of bullets while frantically trying to keep their crosshair on them while they dodge quickly in random directions and nullified any player advantage, and this makes for a poor gameplay experience.