I hate to say it, but I'm in the lukewarm category too. It is too early to grade him, really. Looks like he can recruit. A lot of his coaching decisions early in the season were questionable. Losing so many close games by small margins is not a good sign.
Finally determining out that a major change in strategy -- going big -- was required was a plus, though one could argue he should have figured that out a lot earlier. (I know a lot of people who had been watching Qvale earlier in the season were arguing on this board that he could be an impact player then) Also seems like it took him some time to get the guards to buy into the concept of looking first to pass inside, instead of bombing away from outside.
He deserves some credit for not letting the players give up on themselves after losing so many games they were supposed to be winning.
One disadvantage he has is following coach K, who was a dynamic leader. I don't get the sense that Tinkle inspires the same level of confidence in the people around him. But then, few would.
If I had to give Tinkle a grade now, probably be something like a C+. He's got a lot of room for improvement, but he could pull it off. A lot of coaches have started off modestly and gone on to great things. But given the talent that's being assembled, the fans probably won't look too kindly on him if the team loses ground next year.