Selection pen, which I haven't seen in SAI1, but I might have just been blind? (some don't work like they used to anymore though, for example Luminosity) Layers: there are now layer effects and modes! It's very similar to how Photoshop handles it, with a bunch of possibilities.
TEXT LAYERS! Yasss, the text in this pic is done in SAI2, there's a lot of fonts and you can choose whether you want your text vertically or not
GRADIENT! Yes, we finally have gradient tool! NEW STUFF I'VE NOTICED AND CERTAINLY WOULD USE: I've allowed myself to download and test it, and BOI, DID IT CHANGE! HEY SO did you know SYSTEMAX published the preview version of SAI2? Well, now you do!