Christian Kane took this already really well written character and made him even more well-rounded.
He (Kane) was good as Lindsey in Angel, but - and no offence to the Whedon intended here - I think Eliot was more nuanced. I particularly liked how much of his emotion was 'show, not tell'. Three examples:
when Hardison is rescued from the grave, Eliot's hug was all at once relief, joy and a little anger at the bad, bad family that buried Alec; when he heard that Sophie'd been taking his lessons in combat to heart, his pride was so apparent; when he was being interrogated in the Experiment Job you could see all his gears turning.