SSWR:

OK, how is this for a radical idea: instead of killing off Dooku at the beginning thus having to have general grievous be the new leader of the droid army...why not switch it all up? At the beginning of the movie have grievous be some other villian for some other purpose (maybe he information...maybe he knows where Palpatine/Dooku is...?), Obiwan kills him, Obi and Anakin meet up, space battle, find Palps, kill Dooku, END WAR. From AOTC we already associate Dooku with being in control of the droid army. Remember what Obi said to Anakin in AOTC: "If we catch him we could end this war right now!". With this structure, it's easier for the audience to follow...Why did Lucas add grievous to ROTS?

I by no means haven't figured out the specifics so I don't know if it will work...but that makes more sense IMHO.

this sounds interesting, and would require some new bits being added in. the way i figure it would be reminiscent of how EPIII was originally to start, 'a montage of clone wars battles across 7 worlds', not too dissimilar to the jedi bashing scene later on. the montage could be reinstated (although not necessary), just the seventh world following obi wan specifically.

the exposition could even reveal that palpatine has been missing for some time perhaps? and the scene ending AOTC could lead ROTS?

obi wan could, as suggested, demand from grevious the location of dooku, or perhaps even the details of the secret attack which has been rumoured. cackling with his last breath, grevious utters 'coruscant' at which point kenobi recieves a message from a jedi detailing a massive attack on the city planet.

grevious was the result of lucas asking his art directors to come up with a droid general. i think its generally the result of leading a film production from an art department.