I think what they should do for the 2nd film is have a story wherein Rupert Thorn, Sal Maroni and another man (Grissom possibly, or they can make up a new guy, or maybe there's another man I don't know about or something, but he could be "The Red Hood"😉 are having a feud over who should take over Gotham (including Falcone's men). Introduce Harvey Dent as the new D.A. and focus (instead of a Bruce-Girl love thing going on) on their friendship as the "sacrificial lamb" character.
Say that The Red Hood has a man on his team named Jack Napier (that name I was always fond of, it just seems perfect) who is a complete psycho. Under Rupert Thorne is a Russian arms dealer named Oswald Cobblepot aka The Penguin. To knock Maroni out of the race, Red Hood wants Napier to destroy Axis Chemicals, a major investment under Sal. Batman foils it, and Napier is tossed in the acid vat, thought to have been killed. He comes back and kills Red Hood, saying he always knew he could do a better job than him - essentially, he becomes the new Red Hood, but he calls himself The Joker. Now he has a mob full of men behind him, and he's the leader of a mob, versus Thorne/Cobblepot and Maroni. Joker is insane with this war though, and instead of just putting hits on Thorne/Maroni's men, he just starts wiping everybody out. First on his list is Batman. Insert some "mass destruction" plotline and at the end, Joker is killed in some way where he is laughing (or possibly making others laugh).