Things I liked: I bought this for my kid, although I have been having fun with it, too. The rear sight fell apart after only 2 days, but otherwise the construction is very good. The full auto is a lot of fun, and its easy to walk your rounds in. Mag changes are surprisingly quick and easy.
Things I would have changed: The front grip and the adjustable stock are not the best quality and have a loose fit. Put a good quality holo sight on it and you are ready to rock and roll. Just for curiosity's sake, I installed my Eotech sight off my issued weapon for an afternoon, and it made this shooter a real kick to play with. Nothing like using a sight that cost 3 times what the airsoft rifle cost. I would like to see the battery easier and faster to change.
What others should know: As the owner and operator of real M4's, I can tell you that it DOES NOT feel like the real thing, despite the added weight. The center of gravity is way off. The thing does have great accuracy, although you can tell that people on here are exagerating about the distances they are hitting at. I clamped this thing in a gun vise at a rifle range to sight it in, and it will not consistantly hit a bottle cap sized target at 50 meters as an ealrier review claims no matter what you do with the hop-up.
Things I liked: This sight is well made and has a lot of good features. It is easy to sight in, and holds its position very well, even when used on a real firearm. You get a lot for your money here.
Things I would have changed: I would like an easier way to turn it on and off, and perhaps a larger battery.
What others should know: Don't forget to turn this off. It sucks the battery dead very quickly.