Boss VF-1 Effect Processor

Hi,
I recently bought a used VF-1.  I was pretty excited to get it, but 
now I'm disappointed in the tones I'm getting out of it.  I'm almost 
wondering if something is wrong with it. For the most part, 
the "overdrive" presets (tube, OD, metal, MS, 5150, etc) presets 
sound really harsh and brittle. They don't sound natural at all, but 
rather very digital.  So far, I've mostly been testing it using 
the "line" setting (in the global section of the utility menu), 
although I did try it out through a combo amp briefly with the same 
results.  I've also tested it with a couple of different guitars with 
different pickups.  So do you VF-1 devotees really feel like this box 
produces some convincing tones?  If so, I'm wondering what's up with 
my unit.
Thanks,
Bert