By the way dear gamers, where the heck did this "achievements" thing come from? I have never ever ever cared about a bunch of random external hoops that need jumping just for the sake of jumping.
Well, your rant lumps them all into one thing, which is a little unfair.
There are remarkably bad achievements. Look at MineCraft: you get an achievement for opening your inventory. Idiotic. Other games give you achievements for beating level 1. Hooray!
There are remarkably annoying achievements. These are the ones that reward you for standing in one place for 20 minutes and not doing anything. Stupid.
There are weird achievements that make you go into excess. Dead Rising had a similar one, the need to kill the whole population's worth of zombies, but that also had a tangible in-game reward attached. Not a terrible one, even without it, but one I'd likely never do.
There are challenge achievements. I think these can be fun. Geometry Wars had one of the best ones, where you got an achievement for lasting a minute without firing a shot. It's short so you can keep trying for it without losing any real time and it's challenging and therefore rewarding. Some games do this so poorly, though, and reward you for doing something ridiculously, frustratingly, non-sensically hard, or reward you for beating the whole game without hitting the space key; something that takes hours to achieve and you may or may not know if you're making progress.
Then there are skill achievements. I like these best. These are the ones that sometimes you'll find yourself killing yourself to get (which grows tiring), but sometimes they'll just pop up while you're kicking ass. You won't even realize you're doing something considered incredible until the achievement pops up. When things cool down you'll take a look, see what it was, and think "awesome, I decapitated 50 kittens without taking any damage. I didn't even realize!)
Achievements are what the developer makes of them. They can be awesome and rewarding. They can be stupid or grueling. Overall I feel like they add some enhancement.