Wow - what a discussion we've got going here! Thanks for sharing, everyone. Sometimes it's just nice to come here and see I'm not the only one who cares about these characters and how they're portrayed and positioned in the modern era.
On the original point of poor audience reaction: The comments I've gotten on The Muppets, from moviegoers ranging in age from 6 to 42 (including a surprising number of teenagers), is that they loved the movie. In the days following its North American release, I was over the moon at the frequency with which my FB friends had friends of theirs (with or without kids) commenting on their status lines to the effect of "We saw it the other night and it was AWESOME!"
Now, that being said, this wasn't universal. I've mentioned on this forum that two college friends of mine took their daughters (age 4 and 6) to see it and almost felt sheepish about it afterwards, with the husband suggesting they might have been better off to stay home and watch TMS episodes on DVD and that he was sad that "my kids won't get to enjoy the Muppets the same way I did." Well, no, of course they won't, just like we can't enjoy Looney Tunes or The Flintstones the same way as our grandparents did, or we can't enjoy Sesame Street or the Charlie Brown TV specials the same way our parents did. Life goes on and so do we.
(Footnote to that: His wife later came on FB and said "we seem to be the only people around here who felt that way.")
But, echoing the sentiments of others here, the concept that The Muppets isn't "THE MUPPETS" is absolute nonsense. This movie took the huge risk of trying to recapture the TMS and first-three-movies spirit while giving respect to the new performers and characters that have come on deck since Jim Henson's death, AND creating something fresh and new that would stand on its own. I shudder at the thought of trying to do any of those things, let alone balance the three of them in one movie - and yet, it worked.
And it's still working: I had an animated conversation five nights ago at a local music festival with a friend of mine in his '40s who gushed about the movie to me as if we had just seen it for the first time minutes earlier. (And HE brought it up, not me!)
Finally - I'm not worried about Kermit. He'll be fine. He had his morose sequences in The Muppets (given the break-up of the cast, why wouldn't he?) but as Borples mentioned, he had that great reaction to the Jack Black kidnapping and also had some of his finest moments (inspirational speech at the end) and at least one or two good laughs ("Children?" "Ice cream?" "Laughter?"; to Tex Richman, "Well, you could have just SAID 'No'"). I trust Steve Whitmire with this beloved character and I trust the Muppet brain trust (including Stoller, Bobin and Disney) to give him some attitude when needed.