The problem with annoyingly linear is not that it is linear, but that it is annoyingly so. Done well: Portal, a puzzle game where the whole point is to get from Point A to Point B. Done not too badly: the last level of Portal, where the tile set changes but there is still just the one path and someone has conveniently painted signs as if this too were a planned part of the enrichment center activity.
Done fairly badly: City of Heroes office buildings, where each set of elevators only goes between two floors. To get to his office on the top floor, the boss must walk about a mile and take five or ten staircases (on the strange multi-story floors). The shapes of the floors have no connection to each other, despite the normal outside appearance. Darn non-Euclidean architects. This one is bad in terms of logic and suspension of disbelief, not gameplay; as a gameplay element, the buildings are fairly straightforward tubes of monster to smash. The gameplay problem is when things are less linear, and you must find the last three enemies standing behind a rock around a corner on a small incline on a spur off the third path on the second level, who did not notice when you fired some grenades and a sonic wail at their boss twenty feet away.
Done badly: Garth Agarwen in Middle Earth’s Lone Lands. Garth Agarwen is an outdoor instance, your group’s own chunk of the red swamp. There are a few loops and dead-ends, and a fork separating the two big bosses, but mostly it is a path that winds around itself. It faces the same strange architecture whereby you go through every room to get to the back. It is as if you took all the hallways out of your home and put a door on either side of each room. And sometimes the door is a trapdoor leading to your basement, then up to the catwalk you built near the ceiling to get to the trapdoor up into the bathroom, through the door in the back of the shower into the laundry room, slide the oven aside to get into kitchen, take the door to the kids’ room, out the window into a fenced portion of the backyard, climb the ladder to the top of the shed, then walk across the board into your bedroom window to get your cell phone, which already went to voice mail, dangit. Was that oven-slide a one-way passage? I need to use the bathroom. It might be faster to jump out the other bedroom window and walk around to the front door, assuming the dogs haven’t respawned.
Again, this is not necessarily bad gameplay, although it is annoying to see a teammate just above your jumping height when you know it will take a hundred yards of running to reach him. Could you just throw me a rope? Or when you shoot an enemy and must wait a minute while he navigates all those corners on the way to you. Or when you try to think about the enemy actually living there. Okay, it’s annoying.