De Ronneman said:
I think the best games balance their achievements so that you get about half of them if you play through the campaign normally, and have to try for the other half. If you give people a taste, they'll come back for more.
To the first post: yeah, there are games with stupid "congratulations, you finished level 1!" achievements, but those are usually not games you play more than once...
As Flour posted, you should get some in a play, but achievements are supposed to be awarded for an achievement, you know, something hard. Well, off course anyone can get them, but still, if an achievement is given for bludgeoning someone with a melee weapon, and an achievement for every different meleeweapon(Saw), the game should take a look at it's achievements. Take a game like Team Fortress, that one may even have too many!(and a lot f them are too hard)
Anyway, there's always going to be some easy ones, but a good game uses achievements to give you a good reason to play a game twice.