The G1 series came from the comic so that’s where all of the inspirations, references, and derivations came from. For example, Megatron’s claw-like hand in the first movie was a reference to what happened to his hand in the comic (looks just like it too). Bay was appealing to as many fans as possible and the best way to do that is to stick to a familiar roster, which I thought was a good idea (not giving Soundwave enough screen time was a bad idea though, haha).
And yes, Megatron’s alt mode is actually a big hand gun, and yes, that’s what makes him such a stand-out :). Best not to think too much about how it’s possible because it does push the limits of the show’s sci-fi stuff (mass displacement, mass shifting, all that jazz). At least no one else has such an out-of-this-world alt form. The movie (80’s version) adds more to his character, giving us one of his most memorable quotes. If you’re going to watch the movie, be prepared to see characters getting killed off often.
Red Alert is in the G1 show, or are you saying you don’t like the G1 version? Not sure how he is in the other series, but in G1, he’s kind of a paranoid mess.