Control - having enemies that only race to get next to you and explode, and then having one enemy do that take almost all your health was frustrating as hell. I dont know what remedy where thinking but it was shame design. Its a shame game anyways.
This pretty much in any game is baffling. Its the absolute worst type of enemy, imo
Ok elites with energy swords in Halo Combat Evolved suck!
They decide to charge you and its instant death if they get too close. Can't really shoot them from far away and they eat bullets while charging. I don't know what the intended design was beyond just adding a difficult enemy.
Same goes for all the grenades thrown at you. There aren't any ui indicators for it and checkpoints are frequent enough that I've just accepted I'll die randomly every once in a while. If a sticky grenade hits you there is literally nothing you can do. If movement was better dodging could be a kinda fun mechanic but alas.