Eldest has a more comming of age like story-line much like the last chapter of OotP in the Harry Potter series where harry finally learns of his destiny, and the full implication of it too.....
so it is a much more serious and intense story rather than the happy go lucky plot-line followed in Eragon.
BTW I know this is the wrong forum but talking of eragon did any1 see the movie.... I think personally it was more of a let down as compared to the books.
the plot line was twisted and turned to suit the screenplay....
it was pathetic and way to frenetic at pace.....for a movie based book... no charecter backgrounds, no development of charecters..... even major charecter plot entries were changed......
tejas