I'm not going to rate the film, that's been done to death everywhere else. What I'm going to do is rate the High-Def experience you'll be getting:
Visual: 300 visually is a stunning film. The 'crushing' technique is akin to the graphic-novel counterpart and really sets the atmosphere beautifully. I know very well that such a harsh technique will not appeal to everyone but I will say that without it the film would be left a little lackluster. Moving on to the real High Definition detail: 300 is definitely not the most detailed blu-ray film around; it certainly doesn't show off the true potential of a blu-ray disc (this is more due to the post processing of the film than anything else) but it still looks crisp, vibrant and very detailed. And if I instilled doubt in anyone reading this then please, ignore it. The film looks breathtaking and definitely deserves a 4/5 for visuals alone.
Audio: Deep, clear, haunting and definitely the best audio experience I've had in a while. 5.1 surround sound really immerses you in the experience and makes you feel you are there in the middle of the action. All I need is a red cape and I'm good to go! ;)
Features: I keep reading that blu-ray movies have no extra features or something..I won't go into it but if that's a doubt for anyone here, then drop it immediately. There is a ton of extra features that include deleted scenes, cast and crew interviews, directors commentaries, webisodes (short behind the scenes videos covering everything from makeup and costume design to how the 300 got such buff bodies) and more. The extra features alone would give this film a 5/5.
In conclusion, 300 is definitely a film to add to your blu-ray film collection. Visually stunning with incredible audio to match, and a host of extra features to give die-hard fans a second helping of possibly the greatest action film ever! I'm going to confirm what everyone is saying; 300 is region ABC or regionless (whichever you prefer) and WILL run on UK PS3s. Enjoy!