One thing that is absolutely brain-dead is that (in Chrome) I can't type in maps.google.com and tab-search for my address. I can do this with Amazon.com or Netflix, but not an actual Google property? Weird.
Another thing that is just bafflingly absent is that GMaps doesn't know where my home and work are. Not just as locations, but as concepts. (Snide part of my brain wonders if the Maps team just lives at work.)
Another thing is that to make GMaps work with my Mac, I have to have a Chrome Extension to stop the map from freaking out. And then simple things like double-clicking to zoom in seems to have a non-predictable behavior where sometimes it zooms in and sometimes it tries to put a marker on the map.
Not everything in Gmaps is horrible. There are many nice features. But they've allowed the critical path through the software to become obscured and eroded.