The thing with Gollum is that he still had the Ring with him. Once he lost it, he began to actually age, rather than just change. So him looking cleaner (I thought he looked younger) makes sense (especially considering that he had just been in a lake).
On the subject of humor, I think that Gimli wasn't overdone. I think the humor helped highlight that he was a great warrior, rather than making it seem that he wasn't (except the warg fight, that was just lame). Legolas didn't have that much humor because he was thousands of years old and an elf, so he's expected to be serious. Aragorn has the weight of saving the world on his shoulders and stopping Saruon, so he should be serious. Gimli, however, is a dwarf warrior, whose people were literally made to combat evil. As a natural warrior, he wouldn't think too much of dying, letting him laugh in the face of death and still get away with it.
Also on the subject of humor:
http://i.imgur.com/d3NiH.gif That should make everyone's day.
Gandalf never got around with magic, he used horses pretty much every single time (thus Shadowfax), so I think that Radagast having some way to get around makes sense. Whether it should be a chariot pulled by woodland creatures, I'm not too sure about.
_________________
"Leave Sauron to me."
If you're in the Raleigh, NC area, let me know.