This wasn't that great of an episode. It was a funny idea - Batman goes back in time and meets Sherlock Holmes. Batman proceeds to act like a total dick. That's funny in principle, but not so much in execution. The Sherlock Holmes and Watson characters were just so... bland. They were neither ridiculous and over-the-top charicatures of themselves, nor interesting non-comedic characters. They were just two bland humans with generic English accents. One of the men happened to be wearing a deerstalker - that's how you could tell it was Holmes.
Apart from the blandness of Holmes and Watson, the episode had other, more serious, problems to contend with. Namely: Etrigan the Demon. God I hate Etrigan. He's such a stupid, boring, generic character. Having him speak in rhyme doesn't help matters - it just highlights what a crummy character he is.
There were a few nice bits in the episode - Batman fighting the ridiculous supervillain Crazy Quilt was a nice touch - but mostly it was just not very good. It was all knowingly silly, without actually being funny.