Awesome, but you kind of hurt my feelings when you wrote that the Hulk gave Thor an incredible beatdown. Shame on you.
Here is my idea: I'm stealing your Strucker, Klau, and Vision creation scenes (just imagine them where they should be)
Step 1. Go back in time and kill James Spader's parents.
Step 2. Do not let Vision lift Mjolnir
Step 3. Kill Hawkeye and do it early.
Step 4. Have nothing to do with the mind gem. Instead introduce Wonder Man.
Hydra misused the tesseract and while Wanda and Piotr were successes, wheres Simon Williams (mustach twist) is a double edged sword. His body absorbs the gem and he becomes living, albeit unstable energy. Hydra can't figure out how to separate Simon from the Tesseract without destroying ze verld! So they use him like a battery, siphoning his unlimited energy for their weapons (this keeps him stable, too). When the Avengers show up to rain on Hydra's party, Hydra unleashes Simon - saying he can have his old life back if he defeats the Avengers (lie). Wonder Man does work on the Avengers. In the chaos, Wanda and Piotr are freed. They help protect the peoples. Eventually only Hulk and Thor are left standing. Before they bang, Wand and Piotr talk Simon down and the Avengers agree to help the "miracles".
I don't know how to give Baron Von Strucker a bigger role, but I agree with Dragon that he should have one.
Simon comes back to Avengers Tower and Tony starts to evaluate him. He comes up with a solution to adapt his A.I. program he's working on to continuously siphon off energy from Simon to: 1. stabilize him and 2. power Tony's global protection shield (based loosely on Hydra's operation in CAWS, and developed in secret (we won't even know this is what happened until Ultron goes live). The adaptation would be compact so Simon could live a reasonably normal life (picture Hydray having him hooked up to a giant machine).
AI wasn't ready and it goes full-Ultron; using Simon's energy as a power source and turning Tony's global shield on the world.
Ultron builds himself an unbreakable shell for himself (I do like the idea of Tony having remote control suits; Ultron should evolve from one of those) and Vision to house the energy he can't siphon off Simon (leaving Simon a dying husk). Before he builds Vision, he fights with the Avengers. He beats them very convincingly, killing Hawkeye, but with some reasons to believe the Avengers could beat him if they were ready (For example, Thor isn't there).
Ultron has the same goal he always has; the destruction of the human race. Like the AI he evolved from, Tony's Global Shield is also unfinished. So its a race against time as the Avengers track Ultron down before he can complete the shield and turn it on the world.
The Avengers find Utron and Vision and and EPIC battle ensues. Classic lines are recited.
Wanda turns Vision (some essence of Simon left over or something else?) and it is Vision who delivers the finishing blow: phasing into Ultron's mainframe and control-alt-deleting him.
Back at the Hall of Just...er Avengers Mansion/ Stark Tower:
Thor brings The Enchantress to earth to fix the Vision/ Simon Williams/ Tesseract situation.
Its leaves Vision as an AI (with a glimmer in his eye), Simon with immense, but not as immense power (and glowing eyes), and the Tesseract back to its original form to bring back to Asgard.
