The largest category of achievements is of a type that I would describe as "unavoidable," "patronizing," "noisy," and sometimes even just "nonsensical." Here are a couple good examples from CS: GO:
"Body Bagger - Kill 25 Enemies"
"Shot with their Pants Down - Kill an enemy while they are reloading"
Here's a similar one from XCOM: Enemy Unknown.
"Bada Boom - Kill 50 aliens with explosive weapons"
And again, basically the same achievement for Resident Evil 6:
"Life Saver - Help or rescue your partner ten times"
Ah, the achievements you cannot avoid getting. You're going to kill 25 enemies. Chances are you're going to kill 25 enemies before you even think to check the list of achievements (if you ever do).
Therefore, a lot of players are simply playing the game, and suddenly some information pops up on the screen telling you that you have just "gotten an achievement." This totally meaningless information does not change the game in any way, except to temporarily distract you from the game.
These achievements also do one other thing, however, and that's patronize the player. Did you already design the game to have its own rewards/motivation system? If so, then what is the purpose of having the game to pat me on the back at arbitrary moments? 25 kills? Why is that significant? The rewards that the game gives me are those that I ostensibly have to earn. Not the case for these achievements. You may as well have a timer that doles out a random nonsensical compliment every 15 minutes, such as "you are attractive" or "you've got a great sense of humor."
Without going too far off topic, I want to quickly address this aspect. Those who are familiar with B.F. Skinner's work, particularly in operant conditioning, probably understand that doling out rewards at random intervals, like the current achievement-model tends to, is a well-understood way to squirt happy-chemicals into a user's bloodstream and thereby keep them playing long after they've stopped learning anything. Philosophically, I personally think that games have the capacity to do much more than just be unfulfilling exploitative operant conditioning chambers, but even if you don't, you should be aware that this common system of achievements is causing a similar effect.
The one way that achievements are commonly talked about is with regards to them being an extrinsic reward -- a reward that's coming from outside the system. I join the aforementioned Chris Hecker and many others such as author Alfie Kohn in being skeptical of these kinds of motivators when applied to interesting tasks. Our view is that they take away from the feeling of accomplishment for a task that's already interesting and naturally rewarding.
I'd like to look at this problem in a slightly different way. First, let's take a look at a couple of CS: GO achievements which exemplify the issue I have in mind:
"Three the Hard Way - Kill three enemies with a single HE grenade"
"Aerial Necrobatics - kill an airborne enemy while you are also airborne"
Here's a good one from XCOM: Enemy Unknown:
"Xavier - Mind Control an Ethereal. Single player only."
Let's think about the concept of an explosive grenade in Counter-Strike for a moment. When you buy one, it's exciting, because of the possible destructive potential. If you happen to put one in just the right place, who knows how many people you might kill in one slickly placed move? You may just damage a few people, you may kill one, or you may even kill several. This elasticity makes grenades dynamic and dramatic, and you feel it.
When you throw a grenade, and it actually does kill someone -- or better yet, two, or even three people -- it's a huge rush. All of those times that you got a grenade and didn't use it, or used it but to no effect were all leading up to this moment. A feeling of having gotten better at using grenades -- a grokking of the system of grenades -- is thrilling. You were in a totally unique situation and you made a call that resulted in an almost magical success.
Just then, a little window pops up and tells you that you've gained some kind of achievement. Suddenly, part of that thrill of having done something dynamic and unique is taken away. On some level, you've merely checked off a box -- the same exact box that thousands of other players have also checked off.
The XCOM achievement is similar. What would otherwise feel like a clever "giving you a dose of your own medicine" turns into a "thing you were supposed to do."
I argue that the fact that the developers wrote this thing down for you to check off of a list has a subtle effect of making the event less special. Let me imagine. Let me discover. Let me experience a moment of having done something truly unique without telling me that I've met some developer expectation.
To those who might argue that achievements such as "Three the Hard Way" are needed to get people to even realize that you can kill multiple players with a grenade, you should know that the original version of Counter-Strike didn't have achievements, and HE grenades were very popular. Players don't have to be verbally told everything; some things are obvious and natural enough for players to discover.
As part of my philosophical view of what games are, I have a problem with collection for its own sake. I think that any system that is based on endless collection, or any system where there is collection without a larger purpose is exploitative and uninteresting (and therefore unfulfilling). It's exploitative because it's taking advantage of the biological human need to "gather", and not giving us back anything in exchange for our time. Most games challenge us, stimulate us, move us. Those that exploit us do nothing for us but the cheap.
In a game like Counter-Strike, why exactly do I want to collect all of the achievements? The game keeps track of what "percentage" of the achievements I've collected. Does something happen when I get 100 percent? What is the purpose of keeping track of this information? Is it supposed to impress my friends when they see 35 percent? When they see 95 percent?
And then what about when I do finally get 100 percent? Then what? It's just a dead system hanging off the side of the application? Does it make sense to have a game like Counter-Strike, one that can potentially be played forever, have some exhaustible collection system attached to it?