I really dislike both Four Winds Magi and Shadowdancer for the same reason. They both help you win by damaging the opponent and prevent you from losing by healing your general. I personally think that a card should do one or the other, or at most have the flexibility to do one or the other, but not both simultaneously. A card like Flameblood Warlock is pure aggro and only serves to further your win condition. Similarly, Earth Sphere exists purely for survivability. A well designed card like Phoenix Fire can do one or the other - it can hit face or remove a minion, meaning you can play it for winning or for not losing. The crucial part is that it can do either, but it can’t do both at the same time.
I hate Four Winds Magi and Shadowdancer because they do both simultaneously and have no counterplay on the turn they’re played. If you play Shadowdancer and hit your opponent’s general with 3 Wraithlings, your 5 mana card has just created a 9 health differential that not only removes your opponent’s life total but replenishes yours. I find them to be the most frustrating cards in the game because they serve too many functions at once. Oh, and because they both have decent stats for a midgame minion. I wouldn’t care quite as much if they weren’t 4/4s.
Edit: forgot Shadowdancer’s cost.