I love achievements. Even though my wife says the greatest achievement I have ever unlocked is “most hours spent in front of glowing screens” (that was for Vidmaster: Endure in Halo 3: ODST), I still really enjoy trying to “achieve” these meaningless rewards. It makes me wonder though, have achievements changed how I play games, or was it me who changed?
An example: in Left 4 Dead, once I finished the Expert campaigns, the game began to be less fun. It was okay to run through a campaign, but with no sound effect at the end of the tunnel, I found it less exciting. Same with ODST and the Firefight maps: will I ever go back and play them after I’ve unlocked the achievements? Firefight is a mode I could potentially have seen myself playing endlessly, but I know that thanks to the achievements, I’m not really gonna want to go back after I finish the 200Ks. If those achievements didn’t exist though, I might just keep playing to keep trying to beat my top score. But since achievements arbitrarily define these “top scores” in a lot of games, it takes away my inner desire to beat myself because I know what mark I have to get to to prove to the world my skill.
When I was a younger gamer, I just use to play games over and over because I loved them. I must have beaten Super Mario Bros. 3 like 6 or 7 times, and gotten to the last stage a bunch of other times as well. I used to race against the computer in Mario Kart 64 just for fun (though some of the shenaningans the computer pulled in 150cc drove me nuts), and I even played through the original Halo multiple times just for fun. Nowadays I can’t see myself doing that anymore. It’s partly because I don’t have the time, but it’s also because once I get all the achievements I want, I don’t have the motivation to play anymore. The only exception is multiplayer games I love: Halo 3 and Modern Warfare took up hours and hours of my life and I never really wanted to stop.
I guess in a way achievements made it easier to fit my gaming habits into my changing life habits. Now that I have goals in games to strive for, I can budget out the amount of time I’ll need to play, and that way I can balance my time better. It’s not as “pure” as when I was a kid, but let’s face it: I’m not a kid anymore, and I have responsibilities that are much more important than beating games 50 times. Instead, I can just focus on the achievement for beating a game twice and then go to bed! 
i hear ya…achievements definitely changed the way i played my games – and even changed my buying habits. i ended up deciding to simply sell any games i got all the achievements i wanted out of, thinking that was the best way to manage my game buying/selling. but then there ends up being games that i really regret selling that i had to rebuy (cod4, left 4 dead, bioshock, dead space, etc.). that just goes to show you that while achievements have changed the way we generally play games, there are games that still continue to be enjoyable even after the 1000 – those are definitely keepers!
what’s also interesting is the recent interview with Gearbox’s Randy Pitchford http://www.oxm.co.uk/article.php?id=14388) – he basically claims that games with easier achievements increase sales!