Matt over at X-E has an article up reviewing the Megatron toy from the short-lived Transformers: Generation 2 toyline. He notes that Megatron the tank was a much more useful transformation than Megatron the gun, and I have to agree with him.
I owned the G2 Megatron - G2 hit when I was in the midst of a nostalgic love for Transformers (and even wrote a 200+ page novel about them). G2 Megatron was pretty neat. It was during this time (when I was about 15), that my cousin Mike and I gathered up all the assorted toys we could find in my house and had the last great action figure battle of my childhood. Mike and I both owned G2 Megatron, so we just had both of them lead the bad guys, in comic fashion. In our world, the reason they said "Megatron attack!" is because they were referring to each other. They tortured Starscream and basically wasted time. Meanwhile, on the good guys' side, Optimus Prime attempted to slaughter trick-or-treaters whilst Insane Luke Skywalker spray-painted "LUKE ROOLZ" all over Prime's trailer. (Come to think of it, in this battle it was the Megatrons leading the "good guys" while crazy Optimus was just trying to kill anything in sight.) The battle concluded when Stimpy fired his brain directly in Optimus's grill, defeating him once and for all.