First I have to let you know that I've been a PhotoShop user forever, since version 5.0. I'm not one to switch programs easily and I have yet to switch from PhotoShop to Paint tool sai.
In comparison, jumping into PTS and playing with some of the tools there is some notable things that make life a lot easier. For example they have a complex Pen tool system which allows you to click and then click again to make a line. They have really streamlined this process. For example everyone knows PhotoShop pen tools are clunky, and half assed. This is because illustrator is the program of choice for line work(they aren't going to smash illustrator and ps together, they'd loose money). So if you wanted to have some nice line work you would have to scan your image and bring it into illustrator or start in PhotoShop and then move to illustrator. Not with PTS. You simply specify a layer that you wish to have your line work on, click on your tool and begin making line art. Delve a little deeper and you'll discover that you control the line quality. For example a heavy line may start thick, and then taper off at the end for hair. All of this is based on a click and drag type system. This is something I've been concerned with lately because PhotoShop; although a great bitmap program has been giving me some weird returns even with my Wacom in use. This pen tool is very easy to use and very convenient for someone who wants to really polish their line art digitally.
Lets talk about some coloring. Another big concern of mine recently. Most want their artwork to scream with color and look really nice, finished. Brush textures and 'all that' are great and PhotoShop has a ton of options to make coloring very nice for some. You could use the smudge tool to flex your colored lines blending them together. The thing is, you have to use the smudge tool to do this. PTS has a great watercolor feature which allows one to render one line, then if reworking the same line again with a similar line you will get a smooth output. Ever heard of a game called magna carta? I am envious of the coloring done in this series and would love to achieve that level of skill. I'm no where close to that, but perhaps with this program it would put one a step closer to that type of result.
So what's the secret? I've read that the program uses anti-aliasing based tech to give the user a finer line quality. And while in some areas the program may not be as strong as PS. Obtaining a legitimate copy is around 5000 JPY(yen) or 50$ USD(dollar). Pretty cheap for something you can use to make professional grade work. www.systemax.jp/en/sai/
There is a trial period of 30 days, after that you gotta pay the piper.
Do you use this program already? What do you think of it?