Just had to register, but also a long-time lurker here who's been around since the first episode. That the idea to give a mute character a voice and brilliant (if borderline psychotic and misanthropic at times) cynical character has garnered such a loyal fanbase and following speaks volumes about its creator and his abilities.
For me, Ross isn't just the voice of The Freeman but I've come to expect the character to be as Ross plays him as well: a brilliant, highly intelligent scientist with lots of cheerful facts (not only about the square of the hypothenuse ) and a healthy dose of scepticism. If Valve ever decides to give Gordon a voice, they'll have big shoes to fill indeed.
I fervently hope for a continuation of FM in HL2, although I wouldn't mind a few quick jaunts through the "Across The Universe" idea either - the thought of those shenanigans alone is enough to make me giggle and the ending of HL offers a great jump point for it.
Whatever Ross' next project will be, I'm sure it'll be great, though.