One of the more recent and fastest growing additions to the game industry would have to be the inclusion of an achievement system. During the last GDC Chris Hecker talked about achievements and the danger they could pose to game design. The topic of achievements is an interesting one for me, as someone coming from the days where the only achievement we got was the game over screen. At this point the question of “should we have achievements?" is a moot point, they are here to stay. The better question to ask is “what distinguishes a good achievement from a bad one?"
In my opinion we can group achievements into three broad categories:
1. Grabbed along the Way: These are achievements earned through the normal progression of the game, for ex:" You beat level one", "unlocked double jump" and so on. Basically the player who goes through the game from start to finish is going to get every achievement of this set.
2. Masters Exam: Achievements that require advance skills to get or going beyond the main quest of the game, for ex: " Beat the game on hard", "get a 100 hit combo" and so on. These achievements are usually reserved for players who want to go for 100% or play the game on harder difficulty levels. They can also involve completing a task with an additional restriction or requirement to prove your expertise.
3. Going against the grain: Lastly are achievements that are from the grab bag of sorts. Most often these achievements don't fit with the main game play of the title and either asks you to do something different or something you wouldn't do normally within the game. What could also be almost a sub section of this group are "situational" achievements, these are ones that require a very specific action to achieve which either requires pure luck or a lot of foresight on the player's part.
A few examples that come to mind are : Team Fortress 2 Scout : Kill an enemy in the air, on the ground and underwater in one life, Assassin's Creed 2 : kill an enemy with a jump down assassination while the enemy is poisoned, any game that asks you to beat a level/game without using specific weapons and so on.
With that said it's time for me to go down the list and talk about each grouping. #1 in my opinion is the least favorite as it really isn't an achievement in my opinion. You’re getting rewarded for something that you would have done no matter what. This grouping goes along with Heckler's concern about achievements from the article: "Fundamentally, he explained, his concern is based around a growing body of research suggesting that giving people extrinsic rewards for completing tasks -- for example, rewarding kids for reading by giving them pizza -- decreases the subject's genuine interest in the actual task."
#2 is my preferred achievements as they live up to the title of "achievement", rewarding the player for getting better at your game. These achievements promote replay-ability as most often an average player will not be able to earn these the first time around. Often a side effect of completing these achievements is improving the player's skill at the game which can help them either in another mode of the game or with the genre.
#3 I have mixed feelings about as this is where I've seen the majority of what I considered bad achievements . Team Fortress 2 seems to be the best example of both good and bad achievements. One of the medic achievements was to have the player kill certain # of players with the Medic's close ranged weapon. The problem is that when your medic is attacking people then he's not healing which in a team game is not good. You don't want to reward a person for doing something that doesn’t help them learn the game or play it in such a one off way that after the achievement is finished the player will never do the same thing again.
Some of these random type achievements can be good as a way of blowing off steam but you have to be careful in not making them too random. If the only way to get an achievement is by pure luck then it's not really achievement but just a random event. In Left 4 Dead 2 there are several achievements that require you to perform a specific action, at a specific time in a specific area to get. The problem is that unless you convince the other players to help you or the planets go into alignment, most likely you will not be getting these achievements. The same can be said for ridiculously difficult achievements that require less skill and more an obscene level of min/maxing your play style.
Thinking back my first exposure to an achievement system was actually with an edutainment game, The Logical Journey of the Zoombinis was a logic building game released back in the early 90s. The goal was to lead a band of these creatures called Zoombinis to their new home, the achievement system rewarded players both for getting an entire group to their new home and for getting X # of Zoombinis total. This was an excellent hook for teaching children how to improve their reasoning as once again it rewarded the player for getting better at the game or in this case learning about logic.
A great achievement rewards the player for going the extra mile in mastering the game or giving them something else to go alongside the main gameplay, while a bad achievement doesn't teach the player anything. The secondary goal of achievements is to prolong the play time of your game and for those both good and bad achievements succeed there. I do feel that achievements should be something considered from the start of the design and not something required to be tacked on at the end. This in my opinion is the reason why we see so many achievements based on the first grouping.
Lastly I know this should be a given but it needs to be said, as a designer please make achievements that are in fact possible to achieve without requiring some kind of demonic pact. Beating the entire game on very hard without getting hit and using the basic weapon is a challenge but there is no achievement that is good enough to reward driving your players insane.