Elves having more impressive dexterity than humans is acceptable. So, feats of balance or picking their way through difficult terrain easily (even at top speed) are probably acceptable.
I wasn't a fan of Legolas stabbing two urukhai through the head with one arrow, or taking down the Oliphant and trunk-surfing, nor of his shield-surfing down the stairs...but those feats aren't necessarily impossible so much as...clearly made-for-TV. If I had to pick out the part of super-action-hero Legolas that I liked best.... hmm, I'm not really sure. I don't mind things that look 'cool' just for the sake of looking cool. I just don't want anything to take me out of the idea that this is a battle, not a video game. (of which the running-on-falling-stones was the most egregious)
What really impressed me about Orlando Bloom's performance was all the 'little' minor things he did to make sure he moved like an elf, talked like an elf, etc. He was very deliberate in his motion, and I really enjoyed seeing that. He probably got direction as to what 'be an elf' should look like, but he delivered and clearly took that very seriously. Similarly, in the TV show Sarah Connor Chronicles, actors got to go to 'Terminator boot camp' to learn how terminators move, to make sure that their performances all read as 'a terminator'.
So, yeah, I wanna send our actors to 'elf boot camp' and teach them a bunch of little things that they can all do to read as elves on screen

For Fingolfin's epic fight scene, we'll need a lot more - something much less subtle! But hopefully awesome in a way that doesn't make the audience say, 'aw, c'mon!'
There's a scene in Supernatural 2x04 (Children Shouldn't Play With Dead Things) where they are fighting a zombie in a graveyard at night (as you do). At one point, Dean shoots her multiple times, causing her to fall back into an open grave, and then runs across the graveyard to finish her off. He falls to his knees and slides right into the grave, lands, and stabs her through the heart. So, the bit where he slides on his knees? That's the level of 'cool stunt that looks really smooth' that I'm fine with. It fits naturally into the motion. Sure, in real life, that might not work out so great (good way to faceplant right into your enemy or miss), but can be choreographed to work without someone sitting there scoffing about how ridiculous it is. And for those kinds of small, subtle actions - you need a *lot* of them to prove that elves are elves.
The scene happens at the 4:01 mark in this video. It's brief, but still noticeable (to me, anyway!)
That was the *biggest* complaint about that episode, and their response was, essentially, that people don't know how to use their TVs. Apparently, the lighting wasn't AS bad in HD. Or something.
...As we planned an entire season in darkness, lit only by starlight and lamplight, we maybe have no room to talk
Edit: *crossposted with Amysrevenge*
Yes, exactly! Gotta have Calaquendi being awesome elves in all situations, not just actors with pointy ears being mostly human!