I just love her expression here. Her eyes are, well, very expressive, and that rather small smile is just wonderful. The way her ear is held up, while more or less normal, adds to the expression further. She appears to be guardedly, but strongly interested in what we have to say in a very positive way. I like the shading you did here too—on her irises, on her hair, on her coat. Shadows count, too, particularly easily seen on the neck. And the double-sided mane looks good here. Ah, Twilight, I love you so... <3
Tablets take time to get used to. Don't worry, I had difficulties with tablets at first as well (Here's my first attempt on a tablet if you're interested [link]), drawing on paper seemed so much easier (I still think it's easier) But all you gotta do is practice, practice, practice and you'll get used to the feel of it.
I guess the only thing I would comment about is that when you first use it, it feels kind of glitchy, like, it has a bug or something like that. Though that was before I installed the hard drive/software. After that, it works much better.
I haven't really been able to use it that much recently, so there's still some stuff I'm probably not aware of. But that was the one thing I noticed.