I've been promised that the world of the Shadowhunters will improve as I move throughout the series, but insofar, I am thoroughly unimpressed.
While I'll admit that Clare's urban fantasy underground was somewhat original at its inception, the concept has run rampant since the publication of City of Bones and these forms of subtle, interlaced magical worlds have become far easier to find. The writing is solidly average, though the dialogue has some entertaining lines, and a majority of the characters are stereotypical standees with little development outside of their set "role".
Clary is hopelessly uninvolved and uninformed with her own fate; Jace is a brooding bad boy who gets mad and runs off at every opportunity; Simon, whom I previously enjoyed for being a solidly relatable geeky character, fell into the traps of the "guy best friend who obviously was crushing on Clary for years despite her not having many particularly attractive qualities". I think the Lightwood siblings and Magnus Bane intrigue me the most, but of course their development and characterization is sparse in a book focusing on two characters who might possible be the most boring alive.
I'd like to see more of Isabelle other than the perfect bitch stereotype, as well as some depth into Alec and Magnus as both characters and a relationship, and please god get more into the actual magic of this world instead of just focusing on two angsty whiny sixteen-year-olds with daddy issues.