For me, it's come back to believable. Season 1, flatly No. Season 2... well, there it started getting a bit better, but I credit the addition of John De Lancie for that. The Q / Picard dynamic must have been hard for Stewart to fuck up; the acting equivalent of "muscle memory" was plausibly at play there. Now, in season 3, where he has even more of the old pros to play off of... even better.
I think what I'm getting at is that Picard was Picard in large part due to the rest of the ensemble. But playing against characters who were (in Season 1) fairly unlikable losers -- Raffi was a junkie and the less said about Mizz Barf Bag, the better -- Stewart was just playing A Withering Old Has-Been.
Only now that the old band is back together does it feel like Picard, the character, is back together.