The way they did them is the problem.
Dues Ex remake - Fight in a locked room until one of you drops dead.
Dues Ex - Battle over the entire level, or use kill phrase, or simply run away and fight another day.
I really do miss the original Dues Ex. Wish I could wipe my memory because these remakes are nothing in comparison. Not saying they're bad, just no where near as good.
Great thing about the original as well when it came to bosses - you could do all kinds of things that aren't entirely intended i.e. I've managed to complete the game and leave walton simons alive which actually isn't that easy as if you try and evade him he will keep reappearing infront of you.
Its one of the interesting things about the original game as well in that not everyone is black and white - from one perspective Walton Simons is quite a hateable character from another you can even pity him and potentially see him as a reflection of yourself as manipulated by Icarus.