To be perfectly honest, I found this movie rather funny and amusing for a Disney Channel original movie. Sure, the plot was corny and lame, as was the ridiculous and cliché ending that we all saw coming. But other than that, the characters were all pretty entertaining in their own ways. To me, it's usually the characters that give the movie personality anyway.
The main character, Megan, is your typical spoiled suburban teenage girl who needs to be slapped in the face or else sent to boarding school. Her mother Kathy randomly meets a strange single father named Cosmo who just so happens to have a daughter of his own, Ariel, that is the same age as Kathy's daughter Megan. These two single parents decide to get engaged on a whim and basically thrust together their two very different daughters whose personalities naturally clash. Megan finds Ariel to be weird and eccentric on many levels while Ariel finds Megan to be "evil" as she repeatedly refers to as throughout the whole movie. They pretty much make it known right off the bat that Cosmo and Ariel are "not of this earth," so there isn't much thinking involved when watching this movie. They basically just solve the mystery of whether or not these people are REALLY from another planet by providing no mystery at all and just telling us flat-out, "Yes, they're aliens." As you can already predict without even seeing the movie, Ariel becomes one of two things at her new high school where Megan also attends: a total freak who gets made fun of relentlessly, or someone mistaken for cool and trendy which causes overnight popularity. Well, in this case, it's the second one for Ariel. Now of course, being the little jealous brat that she is, Megan now hates Ariel even more for coming into her life and "taking everything away from her" as she so dramatically puts it later on in the movie, due to this accidental popularity spurt at their high school. Ariel is suddenly a fashion icon, a gifted musician and poet, as well as a "babe" and a trend-setter on many levels once she sets foot at Megan's school. And, on top of all that, Megan's long-time crush Cutter falls for Ariel upon meeting her.
Basically, the entire movie is really just the two main characters, Megan and Ariel, narrating their views on the sticky situation they're in through a "dear diary" form of story telling. Megan thinks the whole world has gone nuts while Ariel thinks Megan is out to get her and can't understand why. Meanwhile, the girls' parents are doing their own thing throughout the movie which is pretty much boring and useless as far as the plot goes.
The real entertainment, at least for me anyway, lied within Cutter's airhead-esquire character's comments as well as the way Ariel managed to become "cool" overnight through doing ridiculous stunts such as wearing a football helmet while riding a bike and crashing into the bike rack upon arriving at school, as well as wearing layers of clothing to "protect her essence," singing strange melodies in music class, and "falling into the sink" to keep her hair looking shiny.
I also enjoyed the hotness of Ariel's boyfriend, who visits in a later scene in the movie. Props to the casting director for picking at least one hot Australian kid to be in the film.
If you like cheesy Disney movies with a few laughs, then see this. Otherwise, I wouldn't recommend it. There isn't much on the lesson-learning level nor is the plot deep or meaningful. It's really just a fun movie to watch on a rainy night in. My rating is 6 out of 10 stars.