Christopher Lee
Ian McKellen
Sean Astin
Anthony Serkis
I thought Gollum was pretty remarkable, actually. I get chills down my spine every time he says, "My precious." I was particularly interested by the scene in Two Towers where he argues with himself.
As for the soundtrack, it's no John Williams score, and I think Howard Shore got somewhat lazy, but the main theme and the Isengard theme were fantastic, in my opinion.
None of it comes close to the Star Wars Trilogy, though (of course). I get really sick of people putting down Star Wars (ever since Lord of the Rings came out), arguing that LOTR is better because it has better character developement (and then smile smugly). Balony! Star Wars has a perfect balance.
But Gollum was really good.