I'm very happy with the way the HD 5150 amp has turned out. It's my favorite amp model on my Peavey Vypyr II amp, and it's now probably going to be my favorite on my HD500X.
Having said that, it definitely needs some tweaks and adjustments to get a usable sound. To my ears, the default settings have way too much mosquito buzz and a little too much low end, but to be honest, the exact same is true with the 5150 model on my Vypyr amp, so I believe that those are just characteristics of the actual amp (but I've not played on a real 5150, so my experience is limited to modelers).
I purposely recorded this clip with the default settings of the amp model to give an idea of the sound without any adjustments. The only exceptions are that I increased the mids about 12%, I added plate reverb and I added tape echo. Also, I did not add drums or bass when recording to let the guitar be fully heard.
So, all of the items that to me need tweaked are still present in this clip, so you'll hear too much buzzyness. But again, this is purposely to give a demo of the raw sound of the amp without much tweaking. I plan on doing an A/B comparison with my Vypyr 5150 settings, which I have set the way I like, to get this more in line with that. Lowering the gain, lowering the presence, reducing the bass and treble a little, and a few other things should get this amp model sounding pretty good.
http://www.mediafire.com/listen/2cxbx2idr74x726/PVPanamaAmpModel.mp3
Edit: I also meant to say that for this clip, I did not change the input settings to guitar/variax instead of guitar/same, so changing that may help, too.