WesternAnimation Excellent
This is very well done. I have absolutely no idea how to add this, but I believe there was a Big No in this movie that you are missing. I'm not sure if this counts, but Phinbella fans everywhere did one just before the credits started rolling.
WesternAnimation Extremely Good
So in a continuing trend of quality for the series, the Made-For-TV Movie does almost everything right, and makes for a good hour and a half of entertainment.
I feel compelled to get the bad out of the way, though, so here's the bad news: The Musical Numbers were way below par this time around. Were this any other children's series they'd probably be well regarded, but thanks to the especially high bar set by this series (My personal favorites being the songs from "Summer Belongs to You" and "Dude, We're getting the Band back Together!") they feel lackluster this time around.
Part of that may be the setting: This is easily one of the darkest stories this series has ever told, and fitting catchy songs into this context probably proved a greater challenge than the other episodes. But unfortunately, the only song I can recall leaving any impact was the dimension-hopping montage, and even then, it's not up to the level usually established by this series.
Fortunately, the lackluster music is more than made up for with a very strong script, which manages to wring believable drama out of what is typically a very lighthearted series. And while the plot twists aren't quite clever enough to surprise anyone, the actual set-up and later execution of those points were fun to watch.
The best part of the movie is the characters, with especial emphasis on the "Earth-2" retoolings of the characters as they appear in the alternate dimension. Isabella as a badass resistance fighter is probably going to be inspiring Deviant Art for months to come (that goes double for each of her Fireside Girls counterparts). This, of course, ignores the fact that Candace-2 pretty much owns every damn scene she's in. I don't think I've ever seen any action scenes quite as visceral as the ones Candace-2 manages to pull off, and Tisdale's rendering of the character as a jaded, morally-questionable resistance leader is just about enough for me to forgive her for having been a part of the HSM trilogy.
So overall assessment: Music is pretty bad (well, in comparison to the rest of the series) but everything else is done so well that I feel no inclination to hold it against the series. And without spoiling too much, there's a lot of shippers who are going to be very pleased with the conclusion of the movie. I know I was.
WesternAnimation Fulfilled all my expectations
I was honestly looking forward to this movie. I loved the cartoon for being a breath of comedic fresh air in a medium that seems obsessed with trying to pass off weirdness AS humor. Phineas and Ferb is a great series, the characters are all strong, the jokes range from usually very good quality to pee-your-pants hilarious, and the songs are a welcome bonus as many are so insanely catchy.
The movie drops none of these elements, takes all the good elements of the cartoon and plays them as best as it can.
Granted, it's not genius per say, but it is extremely good. Better than most TV Movies that I can think of.
One of the reasons I like this film is that I really like the idea of alternate universes because it can open up so many ways to play with your characters in alternate interpretations. While that isn't done much here, it's done enough that I enjoy it. The joke about the alternate Doofenshmirtz's backstory is one of the biggest laughs in the movie I think.
This movie also broke one standard of the cartoon, that the boys never find out about Perry's agent status. While the ending is what you would expect, it's done well and I like it.
The Songs are also good. I find that all the songs are enjoyable, though some are more memorable than others (as to be expected.) "Robot Riot" and "Everything's Better With Perry" are the two I find myself thinking of the most.
The cast is as enjoyable as ever. Phineas and Ferb are their typical kid genius selves and Perry is his typical awesome self. They react naturally to the events around them, though Phineas is given more of a emotional reaction due to Ferb being, well, Ferb.
This movie is a good adventure that contains most of the good stuff that makes Phineas and Ferb the great series that it is.
All in all, I give an 9/10