There was a time (post Catwoman most likely) when the prediction was that audiences were tiring of superhero films. The box office receipts had started to turn a little sour (*cough*Superman Returns*cough*) and the most recognizable characters such as Batman or Spider-Man had already established themselves.
On top of that, common theory was that audiences were getting tired of origin stories. Audiences want the films to get to the good stuff as early as possible, right? Two overpowered muscle heads fighting it out in an epic battle. Transformers certainly managed to get the crowds out with a combination of nostalgia, fantastic marketing, and nearly non-stop massive action. X-Men 3 managed to grab an audience by packing its story full of more characters and more action set pieces.
Therefore, Iron Man had a few things working against it going in. First, the character itself is certainly second tier in terms of comic book properties. The name alone isn't enough to drag people into the theaters. Second, the film is almost entirely an origin story. The character of Iron Man isn't created from one lightning bolt of an event, he's forged slowly through trial and error.
However, it does have a secret weapon in the guise of Robert Downey Jr., who is so perfectly cast as the titular Tony Stark that it's nearly amazing how close he was to not getting the part. The supporting cast - including Jeff Bridges, Terrence Howard and Gwyneth Paltrow - certainly do admirable work, but this is Downey Jr's show and the film is constantly aware of it. Showing the dry charisma he let loose in Kiss Kiss, Bang Bang, Downey fully imbibes a character that he (not coincidentally) shares much in common with.
The truth is, though, that Downey Jr. is not a movie star. At least, he hasn't been for a while. And it would take more than a dynamite cast to get the moms and dads through the door. Luckily, the character is brought to life through some amazing computer effects, combined with Stan Winston's suit, that blend seamlessly throughout the film. Transformers set a new mark for the marriage of real life and technology in film, and Iron Man continues this level of promise. Way back when the original Superman promised that "You will believe a man can fly". With this film, you will believe that a man can build a super powered metal suit and fight bad guys. Not quite as poetic, but the effects stand out by not standing out.
Jon Favreau's direction is workmanlike, but his greatest attribute was bringing this level of talent together in the first place and having a passion for the character which echoes throughout. There are certainly nuggets that only true fans of the character will appreciate (and a nice tease after the closing credits), but this is a film that anyone can watch and enjoy without needing to look up "Iron Man" on wikipedia.
The film is not without its flaws. The nameless terrorist group which captures Stark are generic and slightly offensive, and the film certainly doesn't say much of significance in regards to Stark's guilty conscience about selling weapons to such groups. Bridges chews the scenery enjoyably, but his character is totally two-dimensional and betrays his intentions from the minute we see him on screen. Furthermore, the final battle in the film feels slightly anticlimactic after the hour and a half of buildup that proceeds it.
But these are trifles in what is a superior summer movie, and one that seems destined to kick off what could be a very worthy franchise.