Bill Zebub
“It’s probably Matt Mercer’s fault.”
--- never never never use isometric maps! Top-down only, thanks, unless a side-view would help in which case give that too.
I have to disagree here. I don't think isometric maps are the be-all, end-all, but they aren't terrible, either, and sometimes I really appreciate them. When I6 Ravenloft hit the shelves, the isometric map really helped me make sense of the place. (And I grew up reading floorplans, sections (what you called "side-view"), and elevations: my parents were architects and I was drafting by age 12.)
Sure, sometimes isometric maps "hide" details, but top down maps can also occlude some z-axis information. And while an additional section can solve that, not everybody visualizes 3D well enough to easily reconcile those two views. And even then many layouts will still be ambiguous unless you have two orthogonal sections.
So...you may not personally like isometric plans, which is fine, but they aren't "wrong". It depends on the layout and the execution.