First for the positive.

1: You've got her colors all nice, and smooth

2: And her lines, are also all nice, and smooth

And Now for the negative.

1: Twilight's cutiemark, looks a little off to me, it seems to be missing a few stars.

2: And Twilight's eyes, while good, also seems to be a little off.

Overall, this is a BEAUTIFUL vector, you've did a great job

You should be proud of your vector, and I'll surely add it to my Twilight Sparkle favorites

Actually, if it's okay with you, can I use this vector?

I'll even credit you