What makes the movie so great is the small moments such as the look of complete self-deprecation and low self esteem on Matt's face at the beginning of the movie (watch the scene where he plays Samnang's tape and the close-up on his face as everyone laughs is truly fantastic). 
The facial expressions that Elisha and Emile have are truly incredible.
Many people have already said that she looks more stunning than any woman in any film and that the two actors make the viewer believe that their characters are truly in love. All I can do is agree wholeheartedly.
In many ways it's not a high school movie because high school is effectively over by the time it's started.
Matthew Kidman also has to be one of the, if not the, most complex portrayals of a character in teenage comedy.
Both the script and Emile nail this individual- the type who slips through any major definition and you rarely see in high school movies. He's not unpopular but he's far from cool. Emile's performance is nuanced and clever.
Elisha Cuthbert. What can I say? Ebert said her character was evil and manipulative. Was he even watching the same film? That description sounds like Rebecca DeMornay from Risky Business. Oh, and btw, I don't care whether it's not the original or about pointless 80s semantics, this film is far far better than Risky Business.
Eli and Klitz are so far from the cardboard cut out "best friend" characters you get in most teen comedies.Eli is actually well-developed- a guy who likes to act confident and composed but is terrified and insecure in many ways. Klitz is perhaps even more impressive, with the fantastic Paul Dano (finally getting some recognition after Little Miss Sunshine and There Will Be Blood) making him a real, sympathetic and also funny character within a few seconds and with barely any lines (watch the scene where Matt as student council president makes the Samnang announcement and the way Eli and Klitz aren't sure whether they should clap or not).
Perhaps best of all, the film blends humour seamlessly with emotion". -by luks-11 (Fri May 29 2009). 
-"Did Luke [Greenfield] try to make you watch any of the teen films he grew up on?-Yes. I had already seen "Risky Business" and it was always my wish that we surpass "Risky Business." I was always like, "This has to be better than 'Risky Business.' Let's make this better." I didn't want to re-do it, make it for the ages, I wanted it to be better than "Risky Business." That was my goal from Day One.
-Does it surpass "Risky Business?"
-Oh yeah - in my opinion, a lot more. I watched "Risky Business" recently and I was just - I don't know, I don't know why - maybe it's because I'm competitive with it, I don't know, but for some reason I don't click with that movie".Source: movies.about.com
"In The Girl Next Door, you’ll find a note-perfect tribute to Risky Business, and in Hirsch’s character (Matthew Kidman), you’ll see a modern analogue of Tom Cruise’s Joel Goodsen. 
In Lords of Dogtown — this is where it really gets good — as troubled skateboarder Jay Adams, Hirsch is the heart and soul of the film, absolutely owning every scene in which he appears while retaining no trace of Matthew Kidman. 
His role in Alpha Dog, as rich-kid drug dealer Johnny Truelove, is closer in spirit to his work in Lords of Dogtown, but Hirsch still finds new territory to explore. The character of Truelove could have just ended up as an extended riff on Adams. Hirsch could have tried to shield his image and played Truelove as more of an antihero. Instead, he took the braver path — especially for an up-and-coming young Hollywood turk — and removed every shred of hero from the character. Alpha Dog might not have really succeeded critically or commercially, but Hirsch did".