Star Wars Episode IV

Right. None of that enhances the movie, but at least such things don't change the nature of an important scene.

Technically, until the Emperor disbanded the Senate (mentioned early in Star Wars) wasn't the Republic kind of still alive at least in name if not in fact?

Yes. In fact based on the Revenge of the Sith the Senate was around for almost 20 years. It wasn't until the Death Star was complete in Star Wars that the Emperor disbanded the Senate.

And really it's not hard to see why people would sign up to be Imperial soldiers.

When Palpatine took over he ended the Clone Wars. Of course the galaxy at large didn't know he engineered the whole war in the first place which was why he was able to end it. All they knew was the Chancellor who was now Emperor won the war in the Empires favor. Life was good. Especially for the core planets.

The rebels? Not really a force until Star Wars. It was the destruction of Alderann, a core planet, and the disbanding of the Senate in Star Wars that started to turn more people away from the Empire.

Really at least in name the Empire was only around for an extremely brief time. A handful of years. Though if you read all the Expanded Universe fluff (I know, not canon) the oppression associated with the Empire was around during the latter days of the Republic anyway.

And if you read the Expanded Universe you realize that the destruction of the Empire was the greatest tragedy in galactic history.

As in the real world, the only thing worse than power being in the wrong hands is power being in no ones hands.

The Empire was, however, announced back during the Clone Wars.

Yes we know. But the Empire still acted within certain boundaries because of the Senate that were only removed when the Senate itself was removed in Star Wars.

Being an empire and having a Senate aren't incompatible. Rome, the UK, and US all demonstrate that empires can have meaningful legislative bodies.

Before the PT movies, I'd always kind of assumed that the Republic and Empire were two different alliances in the galaxy, both very ancient, and both uneasily co-existing beside one another, until the Clone Wars, when the Empire decided to move in on the Republic, via using clones to replicate key people in the government of the Republic. The Empire retained the Senate after it conquered the Republic as a sop to those opposed the merging of the two entities.

I never assumed that because Alan Dean Foster's novelization of Star Wars outright said that the switch from "Old Republic" to "Empire" was an inside job and that they were basically the same interstellar entity. And even back then that Papatine had been a senator.