I hate that they make some cards strictly worse then others. They should have some guiding principle with their cards.
Here's an example.
Vampire Nighthawk and Moonglove Winnower.
The Moonglove Winnower isn't even that bad a card, but they're both uncommon, both 2/3 both have deathtouch, but the vampire also have flying
and lifelink, and the kick in the pants? Vampire Night hawk costs 1 less.
Power creep is getting pretty bad. Stuff like Phyrexian Obliterator (
http://www.cardkingdom.com/catalog/item/184399 ) make a lot of cards obsolete.
I also dislike cards where you only gain life and nothing else. Lifegain is a suckers game. You'll just lose it twice as quick if your board position stinks.
I hate cards that let your opponent draw cards, especially ones that let your opponent draw first like Howling Mine. Actually I think Howling Mine is my least favorite card. You have to draw it, play and get the benefit last. So basically before you've made any advantage with it, you've wasted 2 mana and your opponent has drawn two extra cards. Terrible card.