First, plot- SH had a fairly throwaway plot, while GOS tries to be more substantial, with mixed results. Anyone who has read the original stories knows that the plot (besides the mystery of the day)is non-existent. Ridiculous jumps in logic and plot holes abound. The character development of Holmes and Watson is a joy to watch.
Acting- Mixed. In SH, Robert Downey Jr. and Jude Law carry the movie and are just fantastic. Mark Strong as Blackwood is so/so. Racheal Mc Adams
as Irene SUCKS. The girl cannot act her way out of a paper bag. GOS cast is far better. Again RDJ and Jude Law carry the show, but with actual help from Stephen Fry as Mycroft and Jared Harris as Moriarty. And Kelly Reilly finally gets to shine as a kick-a$$ Mary. Naomi Rapace as Sim is OK.
Production- The crazy editing and camera work gets tiresome after a while. On the other hand, the costume design and set design is amazingly good. The score is perfect, and the credits are fun and creative.
Script-Laughing your a$$ off fantastic. RDJ is an unsung comedic genius in his delivery, so that helps. And Jude Law as the (not so) strait man is perfect.
The accuracy to the original source material- Despite the fact that RDJ is decidedly NOT tall, thin, grey eyed, and possessed of a severe facial structure, (as Holmes is described by Doyle), none-the-less he IS Sherlock Holmes. Many people had issue with his interpretation of the character, but taking into account that Watson is a VERY unreliable narrator who is always editing himself so not to offend his stuffy Victorian readership, then Downey's interpretation of the Holmes character not only explains those seemingly out of place elements of Holmes' personality that don't fit in with the traditional interpretations of the character on stage and screen (bouts of mania and depression, drug addiction, erratic behavior,social awkwardness) but Downey's interpretation also reads like the ONLY logical conclusion as to what Holmes is like, sans Victorian era editing for "good taste". Granted, the costume department missed out on Holmes' supposed "personal cleanliness", but this Holmes doesn't look the part already, so why bother? Looks don't matter here, substance does.
There are some debatable anachronisms, and on a whole the films are far more "explodey" then the stories would leave you to believe, but no real complaints.