Although achievements in games may have started off slow in 2005, they have now become commonplace in just about every game that's released. But are they beneficial to a game or do they detract from it? The answer is not an easy yes or no, but there are areas in which they do benefit a game and other areas where they do not.
Achievements really help with making a game more re-playable, as they give you a reason to tone up the difficulty, or try to gather any collectibles you may have missed the first time through. They also often provide challenges for players who maybe didn't want to perform them on the first play-through.
Achievements also give “completionists” something to strive for. It feels great for them to get that Platinum Trophy on the Playstation Network, earn more accessories for their avatar on Xbox Live, or unlock every achievement on Steam.
On the other hand, sometimes certain achievements can stress out a completionist. In Diablo III, for instance, the achievements in most of the categories are fun, but trying to complete achievements in the “campaign” category, where one has to reload an area over and over again to make a location spawn, feels about as good as banging one's head against a wall.
Achievements also especially help with giving players bragging rights. Probably no game implements bragging rights better than World of Warcraft. I myself enjoy showing off by flying around in my Jade Pandaren Kite, a mount you acquire by collecting 150 other mounts! You can also show off by earning achievements that net you titles and pets; the latter of which you can use in Pokemon-style pet battles.
Unlike World of Warcraft and most other games where achievements are no more than just the aforementioned bragging rights, Ragnarok Online 2's “Khara” achievement system strongly encourages players to unlock achievements, as they provide bonus experience to both job and class, as well as give titles which boost stats when applied to the character. Some players may think that this is okay, but others may feel that RO2 is crossing the line here, as achievements have historically been defined as just extra content or challenges that players pursue if they wish. In Ragnarok, it's getting closer and closer to being necessary.
But why do we feel the need to complete achievements at all? In the end most are nothing more but popups that go up on a web site somewhere, associated with an account. Some may mention the bragging rights aspect, but if we want to brag to our friends about doing something extraordinary in a game, we can just brag. It's not as if they won't believe us unless we show them our Steam page (with most friends, anyway). The reason is probably because, like most games, achievements give us an illusion of self-improvement. The more we earn, the more we appreciate our avatar and Gamerscore on the Xbox 360, or our account on Steam, or on Blizzard titles. Like anything in real life, we enjoy being rewarded for our efforts. And although achievements are mostly just pop-ups, it's still enough to make us want to get better and better.