I only had the chance to play with the M16A1 during
basic training, but but my impressions were favorable. It's light, accurate, and how can you not like a gun with parts made by
Mattel! Yes, that plastic/fiberglass stock has the toy company's name stamped right on it.
Hermetic's complaint about an off-center grouping usually indicates that the sight-post needs to be adjusted. This is really an individual adjustment, my setting won't necessarily work for you and vice-versa.
Karmaflux is right on target: The M203 grenade launcher is the ultimate toy. The great thing about the M203 is that the 40mm rounds travel slow enough that you can easily watch them traveling towards their target. After a few minutes practice I could reliably put a shell into the window of an APV at 100 yards.
Of course no military rifle is complete without a bayonet. The M16A1 had one - the M7 (I think the A2's is an M9). Very dangerous little accessory to be handing out. From personal experience let me tell you they keep these things SHARP! I know the day we were first issued it there were lots of trainees standing around with bloody fingers - just couldn't resist the urge to test the edge and find out for themselves.