Once the wadded up paper struck him did the Doctor did he give the Master his full attention, turning to look over his shoulder at him. "You see these eyebrows?" he asked, pointing to his face. "They're good for only two things. Brooding and being cross. It comes with the territory of this regeneration."
In other words, the Doctor was still going to brood, no matter what.
"We were a mess, but I wouldn't want it any other way. Jelpax and Vansell?" The corner of the Doctor's mouth quirked, disapprovingly. "What they did was practically as bad than the Toyroom, and that's saying a lot. Giving up on your ideals, settling for less when you know there's much more to offer. But then again, I've always been known for my extremes."
He fell silent for a moment to look out the window again, then muttered, "You might be right about the games."
In other words, the Doctor was admitting the Master was right.