@Cycloptichorn,
No, he didn't attempt to fight Voldemort and fail... he realized that they both had to die for Voldemort to die. And so he willingly walked to his death. Stood there and waited to die, and was hit by Voldemort's killing curse, and was right on the verge of death, but chose to go back and fight.
I think it would've been unrealistic if in that huge fight with dead people everywhere, they didn't suffer any particular losses. Fred, Tonks, and Lupin were about right... definitely sad, showing the seriousness of this fight (they're not back in "Defense Against the Dark Arts" practicing stuff), and in the case of Lupin, allows him to be one of the reunited quartet that escorts Harry to his death (or so Harry, and they, think) at Voldemort's hands.
What mistake are you referring to re: Voldemort? (I mean he made some, but I'm not sure which you mean by the deus ex machina one... the Elder Wand bit?)
Right, I wasn't saying "A Spell For Chameleon" was the conclusion of the series (and I think that's a series that started far stronger than it ended), just that a twist or deus ex machina or whatever is not something that I think is automatically bad. I think it worked great in ASFC (even if it turns out that in retrospect all that pulse-churning action had a foreordained conclusion), and it didn't bother me in HP.
I found some old threads about this (like
this one) and a comment there made me think of something. By the time the seventh book rolled around there was SO MUCH hype, and expectations were so high, and there was so much public musing about what would happen. I completely sidestepped all of that, wanted to wait to read it until I could with sozlet (what's happening now). So I didn't have any of that raised-expectation stuff re: the last book, it just all came spilling one after another. And I think that maybe some of the book works better in that context.