I can't say much about Heath Ledger's performance that hasn't already been said - I think Brendon of What Would Tyler Durden Do? put it very well:
Everything Ledger did in this movie was fucking awesome. "And here we go" is not an amazing line. Picture that on the page. It's just four little words. Ledger made it awesome. This sucks. I can’t believe he’s dead. Most actors fucking suck. There’s only like 7 good ones. Now there are 6. Now pretty idiots like Channing Tatum will ruin more of my movies, reading lines like his script had the dialog written upside down and backwards. Channing, if you're reading this, and later today you feel a pop inside your head, it's because I just threw a rock at the back of your skull. Hey, look, over here, it's me, Brendon, from that website, You Suck.I will say that I don't think they should recast the Joker. The fact that Rachael whiny-ass Dawes was recast bugged me - the most captivating movie villain in recent memory looking, sounding, or acting slightly differently would just kill any chance of it being as good as this installment. As far as I'm concerned, If Christian Bale and Christopher Nolan come back for a third movie (they are surprisingly uncommitted at this time), Batman should be pitted against other villains.
Now - to the point of this post. I think up to Ledger's performance, audiences have taken this reboot of the series for granted. Nolan's revisioning of Batman has built a solid foundation for the now uber-popular superhero genre in darker territory - allowing for villains to have more weight.
In this day and age where so much of these movies substitute impressive stunts with CGI (though, admittedly, I still like these movies), pander to cheap puns ("Not everyone heals as fast as you, Logan), and break the fourth wall ("I'm the Juggernaut, Bitch"), the Batman series stands apart as legitimately suspenseful.
Now, we all remember the God-awful Joel Schumacher movies. After the box office failure that was Batman and Robin, future Bat-movies were put on hold. However, after seeing The Dark Knight this weekend and being desperate for more, I learned a lot about the prospective follow ups to reboot the series on Wikipedia - Batman Begins came only after several other attempts. So, if you enjoyed Nolan's masterpiece, be thankful that none of these movies came to fruition -
All movies have been drawn from the "Unsuccessful Projects" sub-article on Wikipedia.
Warner Bros. hired Mark Protosevich to write a script for the fifth Batman film, titled Batman Triumphant,  even before the theatrical release of Batman & Robin. Joel Schumacher, George Clooney, and Chris O’Donnell were still contracted for another film.  The Scarecrow was to be the main villain and through the use of his fear gas, Scarecrow would cause Batman to confront his worst fear: the return of The Joker. Harley Quinn was in the script and shown as the daughter of Jack Napier. 
As of yet, the script hasn’t been leaked online and it is unknown whether or not Jack Nicholson would reprise his role as the Joker. Due to poor results from Batman & Robin, Triumphant was canceled and Warner Bros. commissioned more scripts. 
While this doesn't sound like a bad plot (Harley Quinn isn't a bad character if interpret the right way and Scarecrow has and always will be one of my favorite lesser-known comic villains), tone and casting are the concerns with this project. Chris O'Donnell and George Clooney have been the butt of Bat-jokes for years, and that wouldn't have changed with Joel Schumacher at the helm once again. Batman Triumphant would have been junk-food cinema at best - and Batman and Robin 2 at worst.
Another issue I have here is Jack Nicholson as the Joker. Now, it may be because most of us are caught up in Ledger-mania, but I was flipping channels and happened to catch Tim Burton's Batman on abc family. Nicholson wasn't even remotely intimidating or creepy. I realize that half of this was the take on the series, but really - I couldn't watch his performance without being bored to death.
In 1998, Lee Shapiro and Stephen Wise pitched the idea for a fifth Batman movie to Warner Bros. Vice President Tom Lassally. It was to be called Batman: DarKnight (not to be confused with The Dark Knight) and included the Scarecrow and Man-Bat as the new villains, with the studio being most impressed with the characterization of Man-Bat.  Fear was to be the initial theme (much like the main one for Batman Begins) and according to Shapiro, with Scarecrow being true to the source material. Within three months, Lee Shapiro and Stephen Wise sent their first draft to Warner Bros. Joel Schumacher was still signed to direct but dropped out only weeks after the first draft was completed.  The story went as:
Bruce Wayne is in self-imposed seclusion from life, because he feels he has lost his greatest weapons in the fight against crime: his mystique and his enemies' fear. Dick Grayson attends Gotham University, trying to discover who he is apart from his guardian and unwilling to return as Robin without him. Meanwhile, Dr. Jonathan Crane uses his position as professor of psychology at Gotham University and as resident psychiatrist at Arkham Asylum to conduct his experiments in fear. During a vengeful confrontation with a colleague, Dr. Kirk Langstrom, Crane unknowingly initiates Kirk's transformation into the creature known as Man-Bat. The unsuspecting denizens of Gotham scream for Batman's head, believing the Man-Bat's nightly hunts to be the Dark Knight's bloodthirsty return to action. Bruce dons cape and cowl once more to clear his name and solve the mystery behind these attacks. Eventually, Dick ends up in Arkham Asylum under Crane's unsympathetic watch, and Kirk struggles with his "man vs. monster" syndrome as he longs to both reunite with his wife and get revenge on Crane. 
The script for Batman: DarKnight sat at Warner Bros. and languished in development hell up until late 2000. Shapiro stated that DarKnight was in the running the longest as the next Batman movie compared to the other Batman projects in development. 
It may sound somewhat similar to what eventually became Batman Begins, but Man-Bat seems like a mistake for any Batman movie. He is part man, part bat. Seriously. I found it interesting that Scarecrow has consistently been the first choice for lead villain in each of these movies.
In October 1999, the website Ain't It Cool News reported that Warner Bros. was seriously considering a live action Batman Beyond movie, based on the animated series. In January 2000, Ain't It Cool News reported that Paul Dini and Alan Burnett would be writing the script, both of whom are well known for their work on The DC Animated Universe. In August 2000, it was confirmed that Dini, Burnett, Neal Stephenson, and Boaz Yakin were to all write the script, with Yakin to direct. A script was written and turned into Warner Bros., though the project was canceled in favor of the Batman: Year One project. For those of you not familiar, Batman Beyond was the cartoon that had Boy Meets World's Will Freidle voicing Batman. In the future. 'Nuff Said.
Batman vs. Superman
In August 2001, Andrew Kevin Walker pitched Warner Bros. an idea titled Batman vs Superman, attaching Peterson as director. Abrams' script was put on hold, and for reasons unknown, Akiva Goldsman was hired to rewrite Walker's draft which was codenamed "Asylum".
Goldsman's draft (dated June 21, 2002), had the premise of Bruce Wayne trying to shake all of the demons in his life after his five year retirement of crime fighting. Meanwhile, Clark Kent is down on his luck and in despair. Dick Grayson, Alfred Pennyworth and Commissioner Gordon are all dead, as Clark just recently had a divorce with Lois Lane. Clark serves as Bruce's best man at his wedding to the beautiful and lovely Elizabeth Miller. After Elizabeth is killed by the Joker at the honeymoon, Bruce is forced to don the Batsuit once more, tangling a plot which involves Lex Luthor, while Clark sways a romance with Lana Lang in Smallville.
Filming was to start in early 2003, with plans for a five to six month shoot. The release date was set for the summer of 2004. Batman vs Superman was to relaunch both the Batman and Superman franchises respectively, with both sequels being reboots. Within a month of the studio green lighting the project, Petersen left in favor of Troy (2004). Warner Bros. could have easily assigned a new director, but chose to cancel Batman vs Superman in favor of a recent script submitted by Abrams for Superman: Flyby.
Eventually, an adaptation of Frank Miller's Batman: Year One was put into place. It was originally deemed 'too violent,' but not all was lost - this incarnation would eventually be re-arranged into Batman Begins.
I think it's safe to say it was worth the wait.