It depends upon the codec used for the video and the source. Depending on the codec used it might be more demanding when it comes to hardware. Blu-rays use one of the following codecs: H.264 (also known as AVC), VC-1 or MPEG-2. H.264 is the most demanding on hardware but it is also very efficient when it comes to compression ratio.
Blu-rays require one of a few available commercial products in order for you to watch them at all due to copy protection.
Quality will depend on the settings used to encode the file and the quality of the source file.
I've noticed that some movies from the 80's and 90's don't have great quality even on Blu-ray, which would suggest that the original film that was digitized was of poor/average quality, the restoration process was sloppy and/or the encoder and its settings weren't great. The original Blu-ray release of Fifth Element comes to mind (thread with comparison pictures of the first release and the remastered release).