When evaluating a new achievement, it's important for players to ask the following questions:
Who is this for?
Most achievements are targeted toward a particular player group: raiders, pvp'ers, collectors, roleplayers, holiday fanatics, or even "All of the above."
How hard was this intended to be?
Some achievements are meant to be challenging. Some are meant to be easy. It's unreasonable to expect the hard ones to be made easy just because people want them.
How hard is this in reality?
Some easy achievements come out a lot harder than intended and must be nerfed. Others may potentially be too easy and must be buffed.
What are player expectations?
I think where players get really frustrated is when Blizzard decides to give casuals and solo players a run for their money by making supposedly "casual" pastimes challenging, or when hardcore achievements are too easy to satisfy the truly psychotic.
For example, the intention behind the hardcore raiding proto-drakes was to offer a difficult prize to elite players, but these mounts were offered during a period when people were freaking out about the impossible 100 mount achievement. This bred dissatisfaction among the player base when those mounts were removed.
I think Blizzard fails when they focus so much on the challenge of the achievement that they forget about enhancing gameplay. The best achievements have a purpose and meld with the game to make it more enjoyable. The worst achievements actually interfere with gameplay and provide nothing but frustration for the player base.
- Glory of the Hero -- Available for most people but still a serious challenge. Great for those who mostly play with a small group of friends.
- Flirt With Disaster -- Too cute.
- Leeeeeeeeeeeeeroy! -- Most people love this one and it's a great reference to our WoW culture.
- Make Love, Not Warcraft -- Just adorable. :) I like being friendly to dead people.
- All the ones I don't have yet. ^_~
Which ones are your favorites?