Example from World of Warcraft. These achievements just undermine the word achievement. Seeing as it is easy as hell to do all these things why even great an achievement for such a deed.
Another example from Team Fortress 2. Just random achievements and the only reason to do these is to get more points and you gain nothing in return. Waste of time.
The biggest flaw is that they incorporate all easily doable things as achievements, when there only should be the truly hard to do achievements that require skill and determination. Certainly luck is a factor as well but you shouldn't make an achievement because you got an item that had a drop rate 1%.
I like to play games, there are not many who don't. When I was young, I could play a game and finish it and with it comes a certain emotion of satisfaction. Now with all the games that have achievements in them and when I reach in the end it looks that I didn't get all of the achievements done and then there are also difficulty levels like advanced and hardcore is locked. The difficulty settings is one thing I don't like about newer games. When I finish a game on easy and some of my friends did it on hard. Now you wished you did it on hard.
With all these achievements you really can't even finish a game properly because you know you didn't kill that one boss with fists only or didn't do it on hard difficulty.
Overall I think my opinion is probably in the minority. These problems what I have with achievements won't be changed and are mostly catered to the casual players to make them gain points as well but to me it just makes the game longer with no actual satisfaction. You wouldn't do these random achievements because they don't deserve the classification as an achievement but just because they reward you points for that measly deed and that's what makes you do it. I find it's not the right attitude but it probably brings in the most money.