The increased quality is very noticeable with the two classical ones I purchased recently (Naxos Copland Roseo Suite & Rachmaninov Piano Concertos Nos2&3). Although their CD equivalents are good masters in their own right, the quality of the Blurays are stunningly good. They have so much detail and a sense of space around each of the notes, but there's also a beautiful natural quality to the sound. Although there's plenty of slam & that 'wow factor', it never sounds artificial or forced. The format itself has much potential if the marketing departments don't kill it first.
As with many of these format wars, much depends on the quality of the master. I remember making mistakes in the early days of CD buying some dodgy old classical recordings from the 60's: they were never going to sound good.
Looking at the (pretty small) current catalogue of Bluray Audio discs, it surprises me how many releases (particularly pop & rock) are very old recordings. Couldn't they release more recent stuff that was recorded well in the first place? If Bluray Audio's going to catch on, then this pretty half-hearted approach so far isn't going to have much of an impact. My cash is here waiting, but there's very little of the current releases that interests me, which is a shame because I'd happily pay the premium for that sound quality.