You don't think he's good?
I mean I'd be a bit reserved on judging him, because he's only played one full season. He wasn't a starting player before this season. But to be honest the guy was amazing last season, he really took the Ligue by storm. Attacks very well, though his end product in terms of crossing and putting deliveries in, is not that good. But he's a constant threat with his cutting inside and shooting, he's also a very good dribbler for a fullback. Defensively, he does have a tendency to be naive in terms of positioning, but isn't that to be expected for a 20 year old. His one on one defending is extremely good, he's a very hard player to dribble.
All in all, I think and I say this with a lot of caution because after all it's one season, but IMO the next two years will show what he's made off, I will not be surprised if in two years time he's being courted by bigger clubs.
Then again, he could turn out to be another Tremoulinas