Got this two days ago.... I also still own a 51502 head and had an original 5150 combo:
I'd post clips but my computer is ancient....
All the tightness of the first two but has a certain warmth to it which makes it a bit more pleasing to my ear.
I played through a Mesa 2 x12, the EVH 2x12 and both Marshall 2x12 and 4 x12's and preferred the Marshalls.
It really captures that "Heartwork" sound I've always been going after.
I run a TS-9 and an an NS-2 in the front end and an Aphex Aural Exciter / Optical Big bottom through the effects loop which more or less works as a sonic maximizer. Classic 666 settings. Gain at 2 and a half on channel 3.
I am a total bedroom guitar player with two little kids and a 60 hr work week. I've always liked the 5150's at low volumes and this one exceeds my expectations in that dept.
I opened it up a bit but nothing I can really speak to at this point, sounds good. Have to fiddle more with volume. Less gain and effects then probably.
Cleans and crunch are more Fendery obviously but I've mostly played with channel three. I love it.
I was trying not to give in to the hype especially since I have the other head and am not getting rid of it but I am really happy with this amp. My wife not so much.
These kick ass.