Avengers contributions: Thor & Loki Origins / Introduction of Marvel Cosmic Universe / Introduction of Hawkeye / Introduction of Dr. Selvig / *Introduction of the Tesseract
Out of all the lead-in films, Thor arguably has the strongest and most direct ties to the plot of Avengers. However, like Iron Man 2, Thor was also hampered by its dual obligations: building the larger Marvel cinematic universe, and telling a standalone story that introduced both a new protagonist (Thor) and a pivotal antagonist (Loki). Sure, we got to see more of S.H.I.E.L.D., saw The Avengers start to come together when a post-credits scene revealed the Tesseract to Loki - and the brief cameo by Hawkeye (Jeremy Renner) was a thrill for comic book geeks. But on the whole, the second act of Thor was a mishandled affair.
Many of the crossover elements in the film came at the sacrifice of much-needed character development; meaning that when Thor eventually does learn the humility and wisdom he was sorely lacking, the change feels as rushed and unearned as the fly-by-night romance between the muscled Asgardian and the petite Jane Foster (Natalie Portman). It's a shame, really, since star Chris Hemsworth ended up owning the role and achieving breakout stardom as a result of it.
Marvel could've - should've - had more faith, and leaned heavily on their leading man to carry the show (as Jon Favreau did with Iron Man). The story arc would've been complete, the character more fully realized, and Thor would've likely earned more accolades from critics, and more profits from mainstream moviegoers. SPOILER ALERT: Audiences appreciate a good, fun, well-developed story.
As it stands, Thor left a somewhat shallow sketch of the God of Thunder on the screen, and director Kenneth Branagh's departure from the franchise is just another indication that Marvel's tight creative control comes at a sacrifice. While Avengers managed to offer a more vivid picture of Thor (at least as far as his superpowers are concerned), it will really be left to Thor 2 to paint a masterful portrait of the Thunder God.
Verdict: In a lot of ways, Thor is another example of Marvel Studios' growing pains as they learned how to tell proper stories in a shared universe.