If you've already seen Iron Man, then this follow-up is very consistent with it. On the other metallic hand, if you didn't see Iron Man, then you'll probably find little reason to sympathise with this film's central arrogant character of Tony Stark.
For this is quite definitely a sequel.
Some sequels work very hard to better their inspiration's popularity. (eg. Spider-Man 2) Others relax and depend upon it. (eg. The X Files: I Want To Believe)
This one falls into the latter section.
However, although Iron Man 2 runs on lower-powered batteries, I find these slower-running movies to be such a pleasant relief from the usual superhero chaos. The scene in which Vanko attacks Stark while racing at the Circuit de Monaco has the heavy pace of real time, even if said bad guy does take so long that he seems to actually want to lose.
Funnyman Garry Shandling turns in a great performance as Senator Stern, but in so doing breaks the film's believability, unlike Larry King's appearance as Stan Lee, which is only a cameo:
However the biggest problem I had here was Stark's father having hidden details of a new element in some model buildings, without apparently even knowing why his son would one day need it. Surely I must be missing something there...
By sticking to its source material, Iron Man 2 fails to reproduce its originality, however since the first one was so good, that's not such a bad plan, Stan.
Review of Iron Man here.
Review of The Avengers here.
Review of Iron Man Three here.
(with thanks to Alistair)