Basically, 'Reasonable Doubt' is an okay film. If you like thrillers you can certainly do worse. It's one of those films that, if you stumble across it on TV late at night, it's worth watching. However, you probably might feel a little cheated if you paid full price to buy it on Blu-ray, especially as Samuel L Jackson isn't in it as much as most people would probably like.
Best to watch/rent first before you buy.