I've been a Guitar Rig user for a long term, ever since version 2. So I grabbed the demo of Guitar Rig 4. The clean sounds have been improved dramatically, as well as some of the mid-gain amps.

However, the one thing I liked about GR3 – the high gain amp “UltraSonic” - is pretty much ruined in GR4. It used to sound like a ballsy Triple Rectifier. Now it sounds like a bastardised high gain Vox AC30. So if you play metal, I'd stick with GR3.

The virtual pedals have been improved, but still don't sound as good as the real thing. The Big Muff clone actually sounds pretty close to the real thing, provided you pair it with the right clean amp. There's also a Space Echo clone which sounds fantastic. In fact, I might use the Space Echo on vocals and synths in future.

So overall, Guitar Rig 4 gives you a lot to play with, but still falls behind on realism, compared to say AmpliTube Fender. I give it 4/5 stars.

EDIT: I kinda take back the part about them ruining the UltraSonic. It's just that they removed the old presets, but you can import them in from GR3 and it sounds pretty much the same, if not better.
Last edited by BrickIsRed at Oct 6, 2009,
The metal presets suck, exept from God's Love, but a tone i created (see it in my GR4 thread i started a week ago) was actually good.