Iron Man 2 follows on six months after the events of the first film and deals with the fallout of Tony Stark being the living nuclear deterrent against foreign or local powers. Countless other countries and arms dealers are attempting to replicate the Iron Man armour, including Justin Hammer who is hounding for glory and to appease the military. The only person who can replicate the technology though is Ivan Vanko who holds a grudge against Stark industries for the sins of Tony's father.
This, in itself, is a logical progression of the the story and would work well alone. The film does neglect some of the finer aspects of the character development in this story though so it can include a further sub-plot surrounding SHIELD and Tony's health. To comic fans, this does not prove to be detrimental to the overall film and I found myself, along with my friends, rejoicing and fist pumping with every call back or refernce to the Avengers. However, more objectively, this could have been dropped as the second act of the film could prove to be tiresome and irrelevant to a casual movie-goer.
This means that Samuel L Jackson and Scarlett Johansson are both criminally underused and don't have enough substance to really work with. They both do a good job in their roles but may come off as pointless and shallow to someone who does not follow comics. The other actors all do a good job with Downey's undeniable charisma being a delight to watch. Praise also goes to Cheadle for making the role of Rhodes his own and Rockwell and Rourke for their contrasting villainy of flamboyant spectacle and sinister understatement.
The climax of the film provides a spectacular firefight between Iron Man, War Machine and an army of drones that showcases beautifully the differences in their character and technique complimented by the witty banter the two share. Other than a slightly anti-climactic battle with Vanko at the end, the film's action is exhilerating and exciting and doesn't fall into the trap of being loud or obnoxious.
To conclude, Iron Man 2 is, in many ways, a private joke that rewards those well versed in the universe with something exciting, memorable and highly awesome. To others, however, it can be seen as a fun 'summer popcorn flick' that will fill a couple of hours but won't be too extraordinary. Great fun, but perhaps not as good as the first.