You have to be prepared to tweak with the GT6-B. The presets are only so-so at best. The interface for tweaking make take some time to get used to, but after a little bit it becomes natural and makes a lot of sense.
Edit for more comments: I think the pedal is good if you're just getting into effects. A lot of the stuff seems useless, like Dave_W said. The wahs are weak and the synth is really hard to tweak. I'm sure if you spent some time with the synth you'd get a good patch, but it seems to me that it's just way too responsive. That being said, the basic effects are great. There are different models of OD/Distortion, amp models, cab models, and compressor models. It has a pretty tweakable parametric EQ. The chorus and delay/reverb are solid as well. Stuff like the defretter, autoslap, SOS... pretty much everything that's not "normal" seems like it's just there for the fun of it. I like how you can add or reassign footswitch values to either change the, say, drive on the distortion with a stop of your foot from a mild OD to a heavy distortion. Right now I just have mine set on tap delay, and then my extra footswitch pedal that I added is set to turn on a FX2.