I get what you are saying, but part of the fall of Vader was always going to be tied to the cunning of Palpatine and his masterful deception. Now, they definitely should have made Anakin less bitchy about it, but I do like the path they chose.
I'd walk the line. Have Anakin at the end of the second film cast out of the Jedi Order due to Mace finding out about his relationship with Padme, and then Palpatine comes to his aid making him Captain of his Red Guards. Third film rolls around and Palpatine sends Anakin where he knows where Darth Maul is, but Palpatine also tips off Mace Windu. The three of them arrive at the same time, and a 3 way lightsaber fight commences, with Anakin being the ultimate victor. Palpatine then tips off the other Jedis of Anakin's betrayal, forcing Anakin to continue murdering off Jedi and realizing Palpatine set him up for failure.
When he goes to confront him, he realizes that Palpatine is far too powerful for him to take on, and agrees to learn his secrets. Anakin begins planning a new Jedi Order (which aside from a dozen or less has really ceased to be at this point in the war) which would rule the galaxy, with hopefully Obi Wan coming to his side to overthrow the Emperor and then take his position for himself. Obi Wan of course refuses, and so they very reluctantly have to duel to the death. We know how that turned out.