I liked medals, because I like achievements. As long as they're reasonable, anyway.
Basically, unskippable story-based achievements are horrible, as are "Win 1000000000000000000 battles" type achievements, especially if they're multiplayer battles only.
But the vast majority of the medals in this game I like. Such as beating the Elite 4 with a single pokemon, or finding all the hidden grottos, or looking in a trash can despite knowing nothing is in there.
Basically, if it's a challenge of some sort, has reasonable numbers, and / or is a weird quirky yet skippable achievement, I like it. The best achievements changes the way you play in order to get that achievement, or makes you explore places you wouldn't normally have explored before, and several of BW2's medals attempted to do that.
Pokemon White FC: 3568 3549 8596 Pokemon Black 2 FC: 1593 3074 6920