Edit: I went ahead and pre-ordered in time before the first wing opening. I guess I really enjoy the single player games in the adventure mode during Naxxaramas. I read that the heroic mode will not be as frustrating so that'll be good.
Source: us.battle.net
No free first wing this time round unlike Naxxramas but still, if you ever want to spend money on the game, I think it is more worth it to spend on buying the adventure expansion over packs. An individual wing cost USD$6.99 or 700 gold or the equivalent of 7 packs and 7 packs in turn, cost USD$9.99.
The other reason for me personally will be that spending all the money on buying packs does not guarantee a good "return", easily leading to buyer remorse, whereas the expansion is fixed in the sense that you know what cards you will be getting. It is definitely possible to buy 60 packs and not get a single legendary due to the randomness as this is unlike TCG like Magic or Yu-gi-oh where you buy a box and is guaranteed a fixed amount of "Super Rare-s".
There is most likely no doubt that this adventure expansion will be important for all players who want to stay competitive. Ben Brode, the senior game designer of Hearthstone, already stated that each class will get cards that cause huge shift in the meta. (Source: Hearthpwn article) There should definitely be some cards that are relevant and may become staples for some decks as this has always been the case with card games and their card expansion to encourage people to buy them. I am hardly playing Hearthstone nowadays so I will most likely skip the pre-order, forgoing that exclusive cardback and maybe buying the bundle with cash in the future if I get back into the game more.
