I think Ahsoka is adorable. She and the mercenary Cad Bane are wonderful EU characters that the show created.
With that in mind I'm not sure I like the principle behind her addition to the lore. She has practically become like a sister to Anakin and fairly close to Obi-Wan and Padme.
Considering that, it's extremely immersion-breaking to know that she wasn't even created as a character by the time the PT ended. It's just so obvious that she is an afterthought and that they will come with some insanely convoluted reason to explain why nobody mentions her in Episode 3
But the character herself is likeable.