The Marvel films that make up the back stories of the Avengers were produced and created separately by different parties. However the game plan has always been to produce a series that would interrelate to one another. So to better understand the Avengers series it is important to view and think of the films as building blocks that add on to each other.
To this end the Avengers series is quite possibly one of the greatest film projects of modern times. Not unlike the Saw series we see an expansive universe that continues to grow and mature. After seeing each back to back, the pieces fell together that this is something very special.
Each film makes subtle references to the others but more so they reference even things that were not live action films. For example Hulk refers to an incident involving two hunters being injured. This was a cartoon created near the same time where Hulk faces off with Wolverine. Not only do they reference comics, films, and cartoons though—they also reference modern events.
These films are not just pieces of a cheap puzzle shoved together to make weak ties to the others. Each is set with a singular vision of creating a universe. In film this is revolutionary in that only television series have ever successfully accomplished this feat with this many different players, one off productions, and preexisting fans/universe to adhere to.
When view together this rich tapestry weaves a story greater than anyone of the parts. In this way each episode can have faults of its own but as one piece they become something greater.
For this the Avengers receives 5 out of 5 dancing hamsters!