Sketchbook Pro 6, even though it's a somewhat basic program, can definitely produce great work. Look at some of the paintings and drawings done with it and you'll see what I mean. It has a pretty interesting interface, too.
since I have both verisons I can answer this question.
there are a major updates in the SBP 6.0 compared to SBP 2011 (5.1), synthetic paint brush is one of them! and this time color blending and smudge tool are ACTUALLY WORKING in 6.0! not as SAI or anything but still does the job to achive the desirable effects. also, steady stroke is an important feature if you have shaky hands. the french curve tool can be useful too.
Hey Saint, Unfortunately I don't know because I didn't use it before this newest version. I'm sure you could find someone on Amazon who reviewed it who would know, or you could download the demo and check it out. I wouldn't think there would be a big difference in the previous year version.