Anakin has basically been, unbeknownst to Obi-wan, slowly but surely tapping >into the power of the dark side as a means to help win the Clone Wars. What if Anakin’s whole goal was to end the war, and really kinda thought he was a good man, trying to bring peace to the galaxy (words that ring hollow in ROTS as is), which is why he agreed to quickly wipe out the Jedi so that they wouldn’t quickly fall into another war? It’s funny because you can see that’s sort of Lucas’s intent but it ends up as subtext, at best.
That’s how how I would set it up. Anakin and friends (stormtrooper, Ahsoka, whoever) ends up in ever more difficult situation. This happens sometimes by chance, sometimes by the machinations of Palpatine/Dokuu. The dark side becomes Anakin’s easy way out.
However this leaves some things unhandled:
- Anakin’s final change. Amidala’s death is not handled well IMO in the PT.
- Anakin getting recruited by Palpatine.
- Obi-Wan denouncing Anikin/realizing he is evil.
- Obi-Wan possibly defeating Anakin.
3&4 are of course hinted at during the dialogue on the death star in ANH. But it does not have to be Obi-Wan that defeats Anakin. Personally I would have prefered if Obi-Wan desperatly tried to confront and save Anakin in ROtS until he sees Anakin with Palpatine or Anakin doing something that makes Obi-Wan realize Anakin is beyond hope (at least normal hope). It’s a big step going from being someone’s best friend and actively trying to kill them, a feat I don’t think Obi-Wan could perform. Vader could have ended up in a suit after some other combat(s). After all he is supposed to have hunted down and killed many jedi. For continuity at least one such combat should have been in ROtS.
The basic killing of Dokuu in ROtS is actually clever, Anakin ends up in a situation where he is pressed, with Palpatine present. Palp loses one apprentice for a better one. More should have been made of this, it should have been the turning point for Anakin.
So that is how I would have handled it. Basic clone wars setting, Anakin often steaming with battle rage, Palpatine gets “kidnapped”, Obi-Wan and Ahsoka gets knocked out (with a little help from Palp). Dokuu prepares to kill them, Anakin releases his anger and gets recruited by Palpatine. Obi-Wan does not realize this until late in the film, with Yoda warning him. Obi-Wan tries most of the film trying to find a “cure” for his friend, but sees Anakin killing another jedi and walking off with Palp and realizes Anakin is lost, “a master of evil”.