You know one thing I hate about comic-book films such as the Spider-Man films (which I happen to love, actually)? They have villains assigned to the separate movies. When in actuality they should have villains assigned to the series.
What do I mean by that? Well Green Goblin didn't never reappear as a villain in Spider-Man 2... he died, I know... but Doctor Octopus never reappeared in Spider-Man 3 (he died too... although he didn't have to... I wish Raimi would've left him).
Anyway, Spider-Man isn't a perfect example, as each of the villains pre-3 were killed off. But still, there's no sense of villain continuity, like in The Dark Knight. We have Scarecrow to look forward to.
Now, I personally think comic-book films should be more like this... have the main villains and then have the cameos. Like in the comic-books themselves, stop killing off the characters and let them show up in the films more!
The way Scarecrow was done in TDK was perfect... not a big role (didn't take away from Joker that way). Now in the future for Batman 3 we need more villains to just pop up in their own storyline and plot. To appear and then disappear, then reappear in a later film with the same actor.
The Original Batman films:
Batman
The Joker, they killed him off, really a pathetically stupid decision.
Batman Returns
Penguin
Catwoman
They killed Penguin off, thank God. But they never reintroduced Catwoman in Batman Forever, thanks to Joel pooper-schoopermacher.
Batman Forever
They killed off Two-Face, could have saved Batman & Robin (maybe not)... and they let Riddler rot in jail!
Batman & Robin
I discredit this as part of the series...
I'm looking forward to...
Shadow of the Bat
The Riddler (major villain)
Deadshot (minor villain)
Rupert Thorne (mob boss/elected official)
Ra's Al Ghul (at the end appearance)
Talia Al Ghul (minor villain)
Scarecrow (cameo)
The Riddler will be the main villain. Deadshot will be hired by the corrupt GPD members to take down Batman. Rupert Thorne will become the biggest, unseen mob leader in Gotham, while also being a very influencial elected official. Talia will be Bruce's new love interest (under the name of Julia O'Tool, or something) and it will later be known that she is Ra's daughter and that Ra's is alive (Liam Neeson) and that he is planning to destroy the city with nuclear radiation. In a final confrentation Ra's is about to destroy the entire city (along with neighboring cities which will be affected by it), when Talia realizes his plan (she was lied to and thought it was just gonna be the Narrows). Talia kills Ra's and in the process dies herself. Scarecrow will appear (not at the beginning of the film, as are many prequel cameos) but instead will appear like mid-film and have his own seperate plot which is a very small one... Scarecrow will be more like he is in the comics. He will have more weapons to use against Batman and will be harder to beat.
Rupert Thorne will be played by Philip Seymour Hoffman. He becomes obsessed with capturing Riddler because he knows the real identity of Batman. In one dark scene he interrogates him in a real narrow room about the width of Riddler himself! In this rat infested, smelly, cockroach-ridden room he is beat, electricuted and nearly killed. He is then drugged with a high dose of Scarecrow's drugs and is then thrown into that room by himself and the light is turned off. Riddler wakes up insane and a phycopathic genious (he was already a genious). This and a short confrontation between he and Batman is the only screentime Scarecrow will get... That battle will be later...