well like Olaf says, it's 20watter... it won't sound as huge or as tight as a 50 - 100 watt amp, but if you ask me, it's pretty tight already, and very big for an amp that size.
The (+) mode has more gain and sounds a big "bigger" but I like the (-) mode more for rythm stuff, sounds less compressed and more organic..... I love it. Love (+) too but for solos or more modern stuff.