Hmm... unless your guitar has active electronics (e.g.
it has a battery),
you will get a quiet, dull, lifeless sound if you plug it directly into
a line-level device like a computer audio interface.
If I needed to describe the above; how about listening to music from the other side of a
styrofoam wall?
We have a pod here and that seems to take care of the impedance mismatching of the guitar
output to line in. It also helps take some of the load off of the computer since the pod
has it's own dsp.
In the end, it will never sound exactly like a specific miced guitar amp in a specific
location. But, it will sound like most of the stuff recorded in a lot of studios that we
buy on CD.
Some of the direct in/line out guitar dsp boxes aren't that expensive for what they
do. I would suggest going to your local music store and giving them a try. Find a good
electric guitar from their racks, run it into the dsp box, and then into a good mixer. If
they don't have any decent speakers connected to the system, plug a good pair of
headphones into the mixer and listen from there. Some of the dsp boxes have their own
headphone outs, but I would suggest the above as you can mix and match guitars and boxes
until you find a good price/sound quality in the dsp box.