Different situation. Kovacic wanted to leave, period. Ceballos needs to because for whatever reason he can't work with Zidane. Kovacic went on loan because that's what chelsea offered. Ceballos is going in loan because that's what he wants, because he hopes to come back
Anyways, he's a big talent with some really grating flaws. He's a wolverine in terms of energy and hardwork, though by no means a particularly good defensive player he will run and fight his socks off on that side of the ball. In possession he's a tremendous dribbler, too good in fact with a tendency to feck up potential chances by trying one dribbling too many. Good vision and passing range, needs to improve on quality/weight but above all needs to learn timing. Again, he tends to hold on to the ball that extra half sec, take that one extra touch, that can ruin dangerous attacks. He does move the ball well for the most part though. Not a real goal threat but improving in that regard, too. Potential to become one of the very best CM in the world IF he fixes those flaws. If not, he'll be Kovacic 2.0