This one is clearly debatable given your play style, but fast travel took a lot of the magic out of otherwise great MMORPGs ... at least for me.
I can remember a conversation I had over five years ago with a fellow Elder Scrolls fan. He told me he thought it was a huge mistake that Skyrim was including fast travel, and that it was enough of a problem that he would likely not bother picking it up.
I vehemently defended fast travel options that day. I used flying mounts in WoW to state my case. I talked about how I loved them, and that there was nothing wrong with making a game less tedious and more convenient.
But, like a thorn in my side, his argument has followed me through the years. He was right. I was wrong. That's a gross thing to admit, but fast travel clearly shrinks the size and wonder of the game world.
There should be a healthy balance between realistic fast travel like airships and flight points, and the player's access to it. Providing it in abundance just encourages players to skip the majority of a game's content.