The II has a feel and sound improvement over the gen. 1 stuff. New algorithms, higher resolution impulse responses, overall a better and somewhat different beast. It's more to tweaking an actual amp and cab than with the gen 1 stuff.
By no means are the gen 1 stuff a pushover though. I currently use a standard and it works like a charm. But to get a good sound out of it, you usually have to think more as an engineer than a musician with gen 1 stuff. That's probably why I love it as I am a young engineer. I come from a modeler only world. I have compared it to amplitube, line 6, studio devil, digidesign and there is no comparison. I'm not bashing their products. They work and sound well, but when you play and you see all the options there is a very significant difference. But if you are super used to tube amps and aren't willing to compromise a little bit of feel as it is still not a tube amp or you aren't willing to learn the tools, this may not be for you. That's my opinion anyway.