Q: What do most Batman stories have?
A: An assortment of the most interesting villains in comics.
Q: What do Batman stories often lack?
A: A good villain team-up story.
Honestly, aside from Gotham City Sirens, I can't think of many good stories in which Batman rogues unite in an interesting way. Are there any two villains you would like to see team up?
For me, I always thought it would be interesting to see the Mad Hatter and Scarecrow together. Both are very interested in altering perception. I bet together they could come up with some seriously destructive plot for Gotham.