I don't actually dislike it much, but I thought that from a pure design standpoint, it was probably the most poorly implemented feature of the games.
I don't need, or particularly want, a game to praise me for accomplishing mundane tasks, so "achievements" in games just don't appeal to me in general. However, it seems that there are many people who do want just that, and I've resigned myself to that fact. So all I ask of a game is that it implement achievements so that those who like them can easily collect them and those who don't like them can just as easily ignore them.
Fifth gen pokemon failed in that, simply because they chose, for whatever reason, to have that medal guy plunk himself down directly between the counter and the PC, so that he's always in the way. That means that even though I don't care about the medals, I still have to take the time to talk to him every time he shows up just to get him the hell out of the way. That's poor game design.
It's not a big deal - I'm not the sort of person to rage over poor game design, and I just deal with it since it's really only a minor annoyance. But it still is poor design - they could've made it much better simply, for instance, by having him stand on the other side of the counter - to the player's right instead of the player's left. Then the people who actually wanted to talk to him still could just as easily and the people who didn't want to talk to him could get to the PC without him being in the way.