Is it just me, or did the last one kinda sound like Charlie Brown? That's the trouble with using real kid voices, you know... they go through puberty, their voices change. But I see what you mean... they all sound a little different, while DW sounds exactly the same. What I don't like is the new Sue Ellen voice... something's missing.
Anyway, even with the new episodes, the only episode I downright didn't like was that one about the Ocean Zone. I think that one had a new writer who just didn't get the tone of the characters down right.