Since I have beaten down my opinions to a great deal about this issue, I'll keep it simple.
1. Evangelion is THE show that got me hooked on anime
2. To this day, I have not found a show/movie that has surpassed its character development, story complexity, or play on human emotions.
3. Most of the people I have shown Eva to and have watched it completely, have gone out and bought the series themselves.
4. Fanservice? Comon, it's down to a minimum compared to most anime you'll see.
5. This is not meant for young audiences, not because of its violence, but because of its complexity. It takes a mature person to understand it. If a 13 year old is mature enough, by all means go watch it. I know some 13 yr olds who are more mature than some people I know my age.
6. Speaking of violence (and blood), lets be honest with each other here. It's not an action filled series. My first amv was to Eva, and I grabbed every action scene I could find and jammed it into a 4 minute video. Lets see... 650 minutes of footage; 4 minutes of straight action. Nice little ratio. Now I know I didn't get EVERY action shot in the video, but you see my point.
And I'm not talking about the movie, just the series. The movie is a complete different ballgame. But I highly recommend EoE after you've seen the series. If you can handle heavy graphic material, it will answer all your questions. (it will probably confuse you more at first, but watch it again and it'll come together)
7. Eva is NOT all about Christianity, so don't go into it and think "They're making fun of Christianity!" There are plenty of other religions played out in Eva.
Bottom line, it takes someone who's mature in the heart and mind to enjoy this series. Not to mention understand it.
btw, if you want to check out my Eva vid:
http://www.animemusicvideos.org/members/members_videoinfo.php?v=9235
It focuses on the pain/suffering the children must endure while piloting.