The problem I have with Adventure packs/Episodes is half the developers work is already done. The main characters, mobs or enemies and environments are already in place, the lore/story is simply tacked onto the existing 'vanilla' of the first box release, and although the price is less than the full release, you're not really being offered a new experience. A few more levels, a couple more dungeons, all in a setting you've already seen.
Now, you could say the same thing about 'proper' expansions. But with 'proper' expansions, at least you're getting a lot more. A new continent (which is typically pretty big.. hello Kunark and Velious) w/race or class if it's an mmo, new weapons and a longer play time in the case of a FPS expansion.
I like Episode 1. BUT, only just. It skates a very thin line between me feeling it was a good release and feeling I got nickle and dimed. I hope this business model doesn't get too popular, because it represents a good move for developers, but a shit deal for customers.
AP's were why I cancelled my EQ2 account. I recall Brad espousing the virtues of EQ2's AP's, and I'll cancel my Vanguard account if Sigil adopt this lazy arse business model. If they offer lots of cool stuff, fine. But if it's simply a case of tacking a few area's onto New Targanor, I won't just refuse to pay for them, I'll cancel my account. Software houses need to be really careful where they're going to go with this idea. In Half Life's case, if you don't want to pay for it, you can Torrent it -- not that I would advise piracy. In the case of an mmo, people will either not buy it or in my case, cancel the account. I think MMO developers stand to lose more, as they go for the long haul.
Phew, went off a bit there, sorry