Bungie's original net maps were OK for their time and purpose - to get people on the net and enjoying carnage. But, to me, most of them wear thin after a while.
The Second Quest project was a much-needed update to the original levels, adding the right additions to the basic feel of the originals without diverging too much.
Beyond Thunderdome is still a fast moving big ol' arena.
Return to Waldo World has new ramps and ledges that make it even more fun for small frag-fests. It's a bit darker than I like, but it's prettier... staring at the flashing lights over the central pit after being splashed by a rocket is actually kind of fascinating now.
King of Pain and Route 66 are nicely modified. In particular King of Pain gained some much needed complexity making it more of a challenge to splash or be splashed. Route 66 is probably my favorite KOTH level now.
Second Quest is a project designed to remake the original Infinity netmaps, as well as maps from other classic sources (Coriolis Loop and Marathon 2, currently). The end goal was to make them playable and enjoyable, and I believe we succeeded on all counts, with a total of 29 maps so far. It is a collaborative project, including efforts from myself (RyokoTK), screamingfool, Kinetic Turtle, Irons, and treellama.