I have no idea what's up with the bad reviews. This is not a bad film, unless you cannot stand British accents. You will enjoy the numerous contemporary references. There are quite a few sexual innuendos that is better left out, and the opening is not very strong, and there is comedic violence, but there are many, many moments when it allowed me to laugh at the silliness of Holmes and Watson. There is even a delightful musical interlude. And half the places you look, there is good humour. I enjoyed Elf, so I don't mind its silliness.
This film made me laugh quite a lot. I know humour is different for everyone, but I don't regret watching it at all.
However, keep in mind that this film is a parody on Holmes and the characters are very, very different from that in the original story. However, in the end, i was able to accept the characters as they are.
But definitely NOT a family film. And you must learn to be comfortable with ignoring offending portions to appreciate it.
Sad that there is too much crude humour.