I love how nice Skyrim's map look, but it's kind of hard to see roads and such on it... thus partly destroying its purpose as a map. HOWEVER, a 2D map like Oblivion's would make it very hard to make mountains and paths on the mountains properly visible. I think that's why the map is 3D.
So I'm fine with it. I kind of like it.
It's very possible to combine altitude maps with topographic maps. They should've done that, best of both worlds.
Edit: Made me go nostalgiamode, drawing maps of countries I imagined as a kid, with elevation/altitude all very clearly being there. And then it made me wonder if I, as a 8 year old, was thinking more logically than some people at Bethesda.