Iron Man 1 tied into the Avengers, but it was its own film. I even thought that The Incredible Hulk was more of a solid film than IM2, Thor, & Cap. They weren't nearly as bad as IM2 of course, but they still all feel like 2 hour trailers for the Avengers. I don't think Thor or Captain America are really worthy enough to have their own movies. Luckily for them, however, they are part of a cinematic universe, and are pretty darn cool when part of the Avengers. The Hulk is a character that is very hard to sell for a 2 hour film (I mean, a giant CGI monster), though he works a lot more in a television series, despite him looking really stupid by today's standards:
However, TIH was reminiscent to the series, which is still considered a success for its time, and is a big part of pop culture even to this day. The movie's opening was a nod to the opening of the series, and even threw in the "Lonely Man" theme song. Although not a great film, it still manages to have some good action scenes (although pretty few), some good casting (Ed Norton, William Hurt, Tim Roth), and feel like its own movie, while still part of the MCU. Bruce Banner was trying to recreate the super soldier serum that made Captain America, but Captain America is never mentioned, and left for viewers to pick up on themselves. Tony stark's cameo was really cool here, as it just gave enough of a hint to "the avengers."