Look -- it is not groundbreaking. The theme of the world will be destroyed (this time using Norse myth of Ragnarok) and young people will save it has already been done in Riordan's previous series of Percy Jackson and The Heroes of Olympus.... But it doesn't change the fact that I was EXTREMELY ENTERTAINED reading this and getting to know the new characters.
I thought Magnus Chase was more fun to read compared to my first impression of Percy Jackson OR Jason Grace ... My initial impression of Percy in his first book was "he was so bland!" while Jason, for me, was rather clueless (haha!). But Magnus was cool -- he was brave and could be resourceful (hey, he survived being homeless for two years) and funny (I enjoyed his self deprecating humor).
I very much loved his band of brothers (and sister) -- Blitzen (who somehow reminded me of Hagrid), Hearthstone (he was deaf! he used sign language!), and Samirah "Sam" al-Abbas (she was a Muslim girl!!).
I loved other characters too, Jack, Mallory, T.J, and Halfborn Gunderson. Plus the new Norse myth made me Googling some information, with Wikipedia being pretty helpful too *lol*.
So yes, Mr. Riordan, I'm sold. I will be there for the next book in this series.