From an expectation/ability/salary to performance ratio standpoint, I don't think you can mention Green at all, but I think he's clearly been the most valuable, most important player for the Caps in this series. Reflected in his TOI and points, they wouldn't be anywhere without his outlet passes, his ability to get the Rangers' frequent dump-ins quickly out of the zone and into offense for the Caps, not to mention of course his flat-out elite ability in the offensive zone. Best or 2nd-best PP player, which might be the difference in the series, plus his willingness to shoot which seems to be shared by so few other Caps.
Everyone else has been listed, but a guy who's far exceed my own expectations is Johansson. Not because he's been awesome, but because he's better than I've come to expect - which is great skating away from being awful. He's actually done some nice things IMO. It's a shame 8 and 19 have gone long stretches without showing up because I'd like to see if the unit could rekindle some of its dominant form from the home stretch. Mojo looks more willing to mix it up, do some different things, put a body on a D-man, etc.