I haven't been too thrilled with popular music these days, but this song is the only one that stands out to the point where I actually want to take time to criticize it. I haven't heard a worse song in a long time. Let me explain.
First of all, the lyrics. This song is seriously about having a relationship with an alien. Let's put aside for the moment all the absurdities brought up by this to begin with, and just look at the simple fact that it is really a stupid. Why would someone even fantasize, much less sing about, xenophillia? The song is supposedly about love with a foreigner, but I feel like the alien overtones outweigh this claim. It is one of the strangest ideas I've heard of, especially when you consider that we are not presently aware of any alien species such activities would even be possible with.
Next, let's discuss the musicality, or lack thereof. This song has absolutely no musical creativity. The piece is in 4:4 time, which is the simplest of the time signatures (although admittedly some great songs are written in it). However, it doesn't do the song any favors. The drum beat is basically boom-boom-clap-rest for the entire song. When they want to intensify the music, it changes to boom-boom-boom-boom quarter notes. At one point, it has eighth notes on a snare for a measure. That's as far as the drum beat goes.
Outside of the drum beat, it has a strange special effect that puts the listener into the mind of garbled screaming for a half-note duration each measure, only during the "intense" parts. There is a constant quarter-note beeping present through the entire piece that remains unchanged. There is also a strange solid synth note that is present at random times during the song and held out for a few seconds. The only other instrument in use is Katy Perry's voice. The song has absolutely no depth.
In addition, E.T. is not original whatsoever. It is quite auto-tuned, and has a horrendous rap verse edited in, the lyrics of which are even more stupid that the original song's. E.T. follows the generic pop model of "make it about sex and the music comes never." This song is abhorrent, and I wish to never hear it again.

This is one in a long line of musical complaints I have, including many about several popular songs and artists, and MTV. Music of late has disappointed me severely, and this is no exception.

It's symbolism, dude. Granted, it's heavy symbolism, but it's just symbolism. As for the impossibility of it, who cares? It's science fiction. This is a forum filled with people who love Star Trek, Star Wars, Dr. Who, BSG, etc. That's a really weak argument.
4/4 is not the "simplest of the time signatures", it's merely the most common (hence why it's "common time"). Surely 1/4 is simpler. I mean, it's obviously not 11/8+2/16 or anything, but it's not the simplest. Being in 4/4 is in no way a point against a song. As for the drum beat, you're absolutely right. There's absolutely nothing interesting about it.

The rest of this I agree completely. Aside from being kind of catchy, it certainly doesn't have any musically redeeming qualities. Without actually having the music in front of me I can't say 100%, but this song is very theoretically simple--there are no progressions, intervals, or rhythms that stick out as interesting. But do you expect that from pop music? It's specifically made for the majority of people to like it; if it gets too fancy people aren't going to like it as much.

The song was garbage, but I loved the video.

I thought the video was worse than the song.

The song may be auto tuned, but it's part of the theme for this song. Her lastest video (June 12th, 2011, embedded below) isn't auto-tuned to such a degree as her E.T. video. I'm no music expert though, but it's songs like this - beats, the pop-dance vibe - make dance parties so much better.

Everyone has a complaint with MTV.

The common phrase is "one, two. one, two, three, four." It is the time signature that people are most familiar with and that musicians find easiest to play. It contributes to my "unoriginal" point, and I explicitly say that there are a great many songs that are in 4:4 and are fantastic.

As far as "music for the masses" is concerned, the tastelessness of the masses is no reason to produce crappy music.

EDIT: Did I seriously just see Kenny G?