1) Pure stuff - Bauer clearly has some swing and miss stuff (11+ K/9 in at Triple-A), though he only got three whiffs in his MLB debut. This is where the big difference between minor league hitters and major league hitters comes into play. Minor league batters clearly expanded the strike-zone on Bauer's pitches, while the Braves, who have a team walk rate of 8.4 percent, showed good patience overall. Just from a visual perspective, I liked what I saw from Bauer's movement, specifically the tight spin and sharp break of his curve and the tailing action on his fastball.
2) Command - This will be Bauer's achillies heel if not improved upon, especially for the rest of this season. As stated, Bauer walked three and hit a batter and you can see from the BrooksBaseball.net strike-zone plot below that his command within the strike-zone wasn't good either.
Bauer won't be able to leave his offspeed stuff up in the zone at the big league level as he did against the Braves. If he doesn't improve in this area, he's going to frustrate his fantasy owners.
All-in-all, we have a pitcher who has big upside due to his ability to miss bats -- which I assume will show up at the big league level with a few more starts -- but also one that caries some significant risk due to his inconsistent work in and outside the strike-zone. The future is indeed bright for Bauer, but as is the case with any young pitcher, there is plenty of work left for him to do before he reaches his peak.