Columbus' job on the first film was both rewarding and unenviable- rewarding because, well, he got to make the first Harry Potter movie, but unenviable because he felt had to stay as close to the source material as possible to not piss off a built-in fan base that had gained some serious momentum (we were up to Goblet Of Fire in print at that point). For me, the result was a mixed bag- Stone was pretty magical, visually, but lacked its own identity. It came across a little cold to me on my first viewing. I warmed up to it, eventually, but it's still the one I rewatch the least- there are some parts that really drag, right from the get-go (example: did we need Dumbledore to take that long to douse all the street lights with the deluminator?), but I now chalk that (and really, most of the movie) up to Columbus' need to introduce Rowling's world to the uninitiated.
Chamber does some of the same stuff, but, thankfully, Columbus seemed to be having a blast this time around. Like you pointed out, Branagh swoops in and chews scenery in that smarmy way only he can, and Isaacs brings an almost operatic energy to the proceedings with his holier-than-thou evil sonofabitch-ness (seriously, that little scene between him and Arthur Weasley at… Flourish & Botts(?) is one of my favorites in the whole series). It's as if Columbus realized his gamble paid off with Stone and he was able to relax, let his actors do their thing, and concentrate on the fun. Stuff like the pixies scene and the (creeeeeepy) spider colony scene are so very memorable because they're not afraid to be over-the-top. The movie's still a bit too long, but unlike the first (for me, anyway) that doesn't detract from its rewatchability. It's just so damned fun. It makes me wonder where C.C. would have taken the series if he had stayed on as director… but you'll hear no complaints from me about Alfonso Cuarón. Azkaban is still my favorite of the films.
Anyway, this post was too long (like the first two movies! Booyah!), but I blame that on you, E-Rapp. Your write up was so good it made me want to talk Potter. Huzzah!