Well, I'm biased, I know, but I love it when even bosses have some weak points.
Not the usual "weak points" like Achill had, though.
I'm rather thinking now of what I've learned during and through the TDE browser games I recently played.
Enemies - no matter how badass they were - had a tiny chance of doing something that my dictionary translates as a "blooper", "muff" or a "bumbler". They can fall down (with following checks whether the try to get up is successful or not), lose their weapons, even hurt themselves !
But - the protagonist can experience that, too !
During a few fights I experienced (and finall lost them), my "hero" once fell down, but was still able to parry all attacks. Meanwhile his getting-up-checks always failed.
But a few times the opponents could hit him and cause him woulds - whih made the getting-up-checks even far worse - so I lost it.
But I have also seen opponents losing their weapons (and trying a few rounds to get them back into their hands again), and even to fall down !
This was all represented by simple text messages. And rolling dice. Nothing else.
Which means that even non-graphical displays of fightings can be interesting.