Same here, I really can't deal with a "case of the week" show anymore, and this looks like it'll be one.
In the past, Whedon has been very good at mixing case of the week with a strong ongoing story. Most episodes in his previous shows work as standalone stories, but they're also totally connected to everything else that happened during the season. And he doesn't just do this with a scene or two here and there. Usually consequences of things that happened in previous episodes will linger, and the little problems the characters deal with in a given episode often relate to larger problems, either external or internal, that directly impact the season storyline. As a result, later episodes in a season are much more interesting than early episodes because there are tons of subplots brewing by then.
For example, in season 3 of Buffy, many of the early episodes focus on Buffy and Faith: the differences between them, the fact that Faith is a loose cannon, hard to work with. Then the Mayor starts showing up, in a suspicious way, in relation to all the little weekly monster cases. It gradually starts to build towards a big multi-episode explosion at the end of the season. There are several other storylines layered into this (character arcs, relationship arcs, and that sort of thing) and they are all building in the same way with each passing episode, so that the whole thing feels very rich by the time you reach the climax.
I expect this show will be built along the same lines.
edit// to put it more succinctly: you get a new adventure every week, but he doesn't wipe the slate clean. Not even a little bit, and there is always a central storyline building for a season-ending climax.
Somebody above mentioned Veronica Mars, and Justified. Both those shows work the same way, although I would argue that Whedon has been more successful at employing the strategy during his best seasons than either show. Dexter is also built along these lines, at least part of the time.
