It is full size, unlike any toy guns. It's plastic, but it looks really good... you can see it in the photos.
A word of warning though, since 2007 (after I bought this) it has been a legal requirement that these guns are sold with at least half the bodywork in a neon colour so that the guns do not look real. You can still buy these guns online, but they will be two-tone unless you have an airsoft license.
There are lots of blogs and forums giving advice on spraypainting these guns back to black to make them look real. I believe this is against the law and I cannot advise that you should do this. Walking around town with a realistic looking assault rifle is a really good way to test your local police response time. Don't get yourself shot!!!
Here's where I bought mine from:
Be aware of getting an airsoft addiction and building up a huge arsenal of fake weapons. :-)
Why did I buy this fucking thing? I've never used it in a video shoot and it just sits down the side of a shelving unit. Be good to chase off home invaders with though I suppose.