oooh... the thread I wanted to start when this forum was created... there are a LOT of cards I really don't like for a variety of reasons... possession, swindler and saboteur make the list because I feel like I'm entitled to my turns and the cards in my deck... tournament because of the tremendous snowballing advantage it gives the first player that hits the combo... pirate ship because those games tend to take forever, especially when there's no +$ +action kingdom cards... minion because those games take forever as people fish through their decks once the minion "engine" is rolling... king's court because of the massive swings that accompany the actions or lack thereof that it is drawn with...
but there's one card that nobody has mentioned thus far that I really don't like: chapel, which I hate because much more often than not, it's a required buy... in most games, it takes away any other strategic choice... 13 of the top 27 openings involve chapel, nothing else comes close... it might be a little more interesting if it were a $4 card and someone opening 5/2 had to choose between mountebank or chapel, but as things are, there's no need to choose...
if I had to rank 'em, it's probably possession, tournament, minion, pirate ship and swindler as the top five, but I'm pretty much anti-all of 'em...