I'll get em both if I have to. It's jurt that I herd 4th was dumbed down and rigged while 3.5 was convaluded and nerfed some classes.
I still have the megamodule T1-4 Temple of Elemental Evil, and toee is incredibly true to it. You can easily use the map booklet that came with the module to navigate around toee. If you have any specific questions I can answer them.
Hommlett(?) and Nulb are from the module, the named NPCs are from the module, just about everything is true to the module. Toee has some extra content over the module, like the Emridy Meadows area (or is that from Co8?). There are a bunch of extra starter quests in Hommlett, and Nulb is more fleshed out than the module, but the temple... the temple is there in all it's glory. I guess the elemental nodes are greatly shrunk, as they were originally very spacious. There's no missing content really, you just don't have to spend forever walking to the next encounter.
As for D&D, I stopped around 3E. Like Coelocanth I've also played since the late 70's. I like how the stats and xp levels were streamlined, but the class abilities being front-heavy needed to be spread out to account for the new multiclassing rules.