This gun has just arrived and I've had only a short time to play with it. Those reading this review should take the fact that I haven't taken this gun into an actual airsoft battle into account.
Initial impressions were good. This gun is absolutely massive, probably not appropriate for a starter gun. The full metal construction was a huge plus, making the gun feel very solid when you hold it. Because of the ground shipping, some of the screws were a little bit loose, but that was easily fixed. I'd recommend double checking all of the screws, even the ones for the cosmetic stuff like the feed cover.
The sights work pretty well and are completely adjustable, up to about 33% for windage and the same for distance.
The FPS on this gun is good, with mine clocking in at 351 FPS (I haven't tested this myself). More impressive than the FPS, however, is the rate of fire. I haven't tested the rate of fire either, but when firing the gun, it looks like the BBs exiting the barrel are a solid white line. This means that you're going to be putting quite a few rounds on whichever target you're aiming at.
One of the small issues I take with the M249 is the box magazine. As far as I'm aware, the auto-wind function doesn't work, so you'll have to hit the manual wind switch every time your ammo runs dry (although I am of the opinion that it adds a bit of realism to the game). That, and like the rest of the gun, the box magazine is enormous. If you're not at least six feet tall or have arms as long as a garden hose, odds are, you're going to have trouble holding the thing like a rifle with the box mag attached. I got around this problem by removing the box mag when I'm not in a static position (defending a base, flag or whatever) and sliding in an M16 high-cap magazine (which I also highly recommend you purchase) whenever I'm on the move.
The gun isn't without it's flaws. Like several other reviewers have mentioned, the integrated bipod isn't great, and should probably be replaced. At least two of the people who bought this gun had an issue with the trigger mechanism, although I'm given to understand that it's easily fixed (see L. HOUGH JR.'s review on the first page). The battery the gun comes with is of okay quality, but a 9.6v with at least 2500mAh would probably serve you much better. The M16/4 magazine this gun comes with has a small issue as well. I tried sliding this into a friends JG M4, but it wouldn't fit. We figured out that the ridge on the back of the magazine is about 1/16th of an inch too wide, but some filing and a fresh coat of paint solved that (other mags fit just fine into the M249's magazine port).
Overall, I very highly recommend this gun, but it's definitely not for a beginner, nor is it for anyone who is a bit shorter than average.
Multiple magazine options
Super high capacity box magazine.
Price (but you get what you pay for)
Slight problem with the included M16 magazine
Battery should be replaced
Rating: [5 of 5 Stars!]