I have 2 of them, one with & one without home cinema.
I think the sound is perfectly acceptable from them - not awe inspiring but acceptable.
Put it like this, I haven't sat there once and thought about the sound quality so it can't be that bad. I have it set on "music" which seems to beef it up a little bit.
As said before, at this TV size HD is not a big issue and the TV looks great in SD or HD but I've not got Blu-Ray so I can't comment about that.
There is however this What HiFi review which talks about Blu-Ray
http://whathifi.com/Review/Panasonic-TH-37PX80B/
PX80, PX80 so good I bought it twice 😀