I don't do metal, or any genre that might need high gain amps. I have the first Grind Machine, and must admit I seldomly if ever use it. I have several amp sims (Revalver, Amplitube, Guitar Rig, all the free amps available right now, a Line 6 Pod XT, and a Yamaha DG Stomp, you get the picture).
This amp sim is nothing short of amazing. Yes it can get heavy and shreddy (it's a high gain amp suite after all), but it can also do more 'subtle' lead tones, crunchy rhythms, cleanish slightly driven tones, and with the expansions, Hidden Gems in particular, you can even play jazz and blues with it.
A slew of high gain amps, along with several cab options and the 'tight' button make Grind Machine II an essential, versatile production tool ideal to get if you're into guitar music.