So the Joker has 20 pounds of green Kryptonite and wants Luthor to buy it from him for one billion dollars- after he kills Superman. Batman takes a trip to Metropolis and the fun begins.
Not only do our heroes not see eye-to-eye, our villains don't exactly get along either. One of the best parts is Luthor and the Joker having a meeting while Harley and Mercy fight back and forth across the screen in the best tradition of old Merry Melodies and Loony Toons. You never even see them fighting, you hear it, and then there's the aftermath when Lex leaves.
All in all it's a great story, with the possible exception of Bruce romancing Lois and how quickly it happens. Add into that her discovering Bruce is Batman... how many people know his "secret" ID now? I can think of at least seven, and eight if you believe (like I do) that Gordon has it sussed as well.