I've mostly had good luck with blister packs. Had a Flarion ex in the last one I opened for instance. Usually the promo cards are terrible but they nearly aways suck my sons in. "Oh, wow dad! Look Raikou! Let's get it!!" Then they get disapointed that the card can't really be used in any sort of reasonable deck.
What I don't like are the ones that have "extras" in them ... like the ones with 15 card sleves ... that cost extra. Blegh.
I've also recently seen a LOT of non-offical blister pack things that have a bunch of loose cards in them. These things are created by some third party and they mix all sorts of cards from different sets, including WC promo sets, and package them together. These strike me as very unethical to sell in a big box store since so many folks will have no idea what they are buying.
