I'm loving this amp! I had a 5C, which I adored, as I was just looking for a simple low-watt tube amp for practice and recording (you can see my review of that amp). And it was great. But when I compared specs with the 20C, there were many features I wanted in an amp that I didn't have with the 5C. Like, a 10-inch speaker (the 8-inch Celestian in the 5C is highly regarded, but I didn't like it), 16 Ohm and 8 Ohm speaker outs, a presence knob (like my old Plexi), a master volume, and 3 power settings - 20W, 3W, and .5W. Tho I have to say I think the rating for the .5W is probably wrong - it's way loud at that level. So, this amp is loud enough to play small to medium clubs at 20W, and can be over driven at .5 to 3W for recording and practice. It also has a direct out for inserting directly to your DAW (from the preamt stage I guess).
The tone? Very, very good. It breaks up anywhere you want it too, but also sounds great clean. Lots of highs and high mids. It takes pedals really well - compressors and drive pedals help with low volume over drive, and there's an FX loop for time-based pedals. My criticism of the access to the outputs on the back of the amp remain the same...Very difficult - but if you go with the head instead of the combo, that's much easier.
All in all an amazing Marshall tube amp at a ridiculously low price. Tone to the bone, as you would expect from Marshall.