Tricky, what do you think of as 4e's strengths?
This was directed at Tricky, but I'll jump in to say that - at least for me - the strengths of 4e are:
* Interesting set piece battles. I'm not opposed to having one or two regular fights per level, just to make sure there is enough action and so that the PCs get to use all their powers. But, mostly, each fight should be to accomplish a purpose and should involve some sort of interesting opponent, terrain or situation.
* Fun powers. The PCs get a lot of fun powers as they level up. There should be feats, prestige classes and maybe some special powers to tie the game world into the characters. (Also, as I noted above, there needs to be enough combat that the PCs get a chance to use their combat powers.)
* Flexible adventuring days. Because 4e can better handle a large or small number of encounters per day, the AP can focus on story / world concerns more than resource management.
* Skill Challenges. OK, as published by WotC, skill challenges are a poor mechanic, but there is a lot to be said for a mechanism to handle non-combat encounters with more than a single die roll. I've had a lot of fun with the Gate Pass skill challenges (OK, with some editing... and my players skipped Kiki). I found the key is to have enough information in the skill challenge about what is going on in-game so that the players can engage the in-game problem that their character's are working rather than the out-of-game problem of just getting the right skills in play. I'm not sure I have the math right, but I tend to use +/- 5 or 10 modifiers for particularly good or bad ideas. Yes, the modifiers are huge, but you want identifying a great in-game solution to be the optimal way to solve the challenge.
...and, of course, there are also WotBS's strengths: meaningful decisions, interesting NPCs, shades-of-gray morality, flavorful world, non-dungeon-crawl. It would be nice to better use the strengths of 4e, but don't lose what makes WotBS great!
-KS