I thought it was pretty good, but you could definately tell when something wasnt right..
BD Movies i have:
Batman Begins
The Dark Knight
Ironman
Rambo
Star Trek
Inglorious Basterds
The Incredible Hulk
Speed Racer
Pandorum
Terminator Salvation
The Hangover
Live Free or Die Hard
3:10 to Yuma
The Fast and The Furious (4)
There are a few i know i am missing.
As far as older movies that may be your favorite, DO NOT spend the money for them on Blu Ray. Standard DVD will be just fine.
You must remember that up until a few years ago they were filiming in standard def cameras. So when they take these movies shot in standard def and convert them up to HD its pointless. Stick with the movies made after Blu ray was on the scene.
PS: 300 can also be bought on regular standard def. You will be very disapointed with it on blu ray, trust me. Its so bad you can tell when they stand in front of a green screen.... o wait.
EDIT:
On a good quality Blu Ray disk like Transformers is on. Not some cheap crap Blu Ray disk thats not really any better than a standard DVD like many of the Blu Ray movies out there.
I just got Shooter on BD. It looks good, generally I think a BD is good when I watch a movie that Ive already seen on standard def and I notice so much more detail in the background etc, things that I never noticed before watching the movie on BD.
Star Trek was the first BD I purchased. Seems like it was a good choice as everyone is unanimous that it doesnt get much better. I also have District 9 which I hadnt seen mentioned and its pretty good too.
Just remember, just because it's on Blu-ray doesn't mean it's better than the DVD version. Some of the Blu-ray transfers suck. A good up-converting player will look as good as a sucky Blu-ray transfer. Look for reviews of the Blu-rays you want to buy before spending your cash.
A lot of the animated movies are excellent on Blu-ray and are reference material (audio and video are so good it can be used to showcase a set up), like Up, Bolt, Monster's Inc., Cars, etc. Not all of them are great though, but most of them.
Other great movies have already been listed, like Transformers, Star Trek, Iron Man, and the Dark Knight. Some other good ones are Inglourious Basterds, Quantum of Solace, Sin City, The Taking of Pelham 123, and Watchmen. Those are some of the movies that IMO are worth buying the Blu-ray over the DVD. Just look for reviews online of the movies that you want and you should be good to go. Enjoy your new set up!