Not a fan of the shoes in both. They don't give me a sexy or sophisticated vibe. Feel like something a teen girl would wear, could've done with something more naturally and gently curved. Anatomy wise the distance between her hips and breasts seem a bit odd. Other then that nice expression on her face and while I'm not a fan of the hairstyle (I like woman's styles that have their hair a bit wilder and freer) you did a very very impressive amount of detail on the hair with some quite nice detail on the individual strands.
As to the second picture most of the same criticisms apply. Adding on to those tail doesn't seem "alive" enough. Maybe if you had it manipulating something or in a more interesting position it'd be a stronger feature. With all we've seen succubae in this story do with their tails could use something more with it, or perhaps showing some of the filaments it possesses? Other then that nice horns. Remind me a lot of
Alexstrasza from Warcraft but they do look quite nice regardless of if that is your inspiration or not. Nice work on the glasses too but kind of seems like the color from the eyes slipped on to the glasses a bit which is a little distracting.
A general criticism of your work is that in many of the pictures I've seen this artist draw I've always thought the mouth could be more descriptive. A bit of teeth showing or smaller lips but a more animated expression of them could really elevate the art quite a bit.