Good jobs take advantage of your strengths. Great jobs take advantage of your weaknesses.
A system that is bad design in most games can be a great feature in a game that consciously builds around it.
For example, Darkfall used the slowest, most inconvenient looting mechanic available. You opened up your inventory, you opened your target’s inventory, and you dragged items one at a time. Why do this when most games were moving towards fast looting of entire groups of enemies with a single keystroke? Because Darkfall was a PvP game where you were meant to be vulnerable while looting your victims. The inventory screens blocked your vision, looting took time, and people died because they got greedy. It would be a problem if you could gank someone and grab all his stuff at a flat out run without stopping. If you waylaid a lone victim, loot at your leisure; if he had a bunch of friends, now would be a good time to start running, and no you do not get a loot reward for suicide-attacking a large group (idiot).
For example, long travel times are great design when places should be far apart. If the boss is next to the respawn spot, you get the death zerg effect. Respawn placement is a critical factor in PvP fights, along with the respawn timer. If killing someone does not meaningfully remove him from the fight, you may have a problem here. In either Guild Wars, you can teleport most places instantly, so the few places that require significant travel are meaningful (or completely ignored and meaningless; you can build consciously but badly).
“THAC0 kept the riff-raff out.”
Some developers and/or players want a niche product just for “us.” Barriers to entry can be intentional and a feature from the perspective of the desired user. Some games are not user-friendly because the developers will happily take less money in exchange for not dealing with the kind of people who need user-friendly games. Some of the worst communities out there value your feeling unwelcome in their cesspools.
On a less extreme scale, tastes differ, and catering to one market involves ignoring demands to cater to another. Yes, most people want X, which works out nicely because there are already 100 companies selling X; here, we sell Y to people who want Y. Making Civilization more like Farmville will ruin Civ without capturing the Farmville market. We already have a couple versions of WoW in space, so EVE Online merrily captures just about everyone else by making design decisions completely at odds with the market leader while others copy and fail. There are many things that EVE could do better, but its strength has been identifying what it needs to do well (and its worst times have come from failing that, not from its systems that are lousy or entirely missing).
Let’s break at this point and come back tomorrow for a consideration of “bad at” and “bad for.” In the meantime, feel free to toss in your favorite example of “this would never work anywhere else.”