Iron Man 2 is much the same of its predecessor. Iron Man (Robert Downey Jr.) has to fight another humanoid - this time War Machine - and has to overcome personal problems and medical difficulties in order to battle his enemies.
When the first Iron Man came out, it entered a saturated market with plenty of other heroes and it came out on top thanks to its smart humour and interesting protagonist. Despite being a new character, Iron Man was still very warmly received.
Iron Man 2 takes this successful formula and very much recycles it. There are more pieces added in for the fans, while it still keeps its accessibility for a broader casual audience.
Where Iron Man 2 falls down is that it feels very much like a stop-gap in the franchise before The Avengers - exemplified with the introduction of Scarlett Johansson and Samuel L. Jackson. Their characters were interesting but they weren't given enough screen time to really have an impact. It really does feel as though they have been jammed in to try and justify their inclusion in The Avengers.
The one positive that this film gives over its predecessor is that is that it has a proper villain - and someone with a dastardly plan that doesn't involve around a business plan to overthrow Tony Stark. Mickey Rourke's Whiplash is mysterious and interesting while his change in character from focused workman to utter maniac is outstanding.
In summary then, Iron Man 2 is still just as witty as the original, but its lack of originality and its seeming conformity to the genre are not what Iron Man fans should expect.