Nearly all of the decisions he made is wrong.
First off, Alex Corbisiero has been reinstated into the starting lineup. Correct call by Rowntree. Corbisiero was a positive influence in the first test, and is by a distance the best scrummager left in the squad. That Mako Vunipola is the backup is probably an ok call, given the impact he brings. He has had a good tour, and wasn't too bad last week aside from the early scrums.
Hibbard for Tom Youngs is a further attempt to dominate the scrum. Possibly a good call, but Hibbard's lineout throwing has been terrible, so I'm marking this one down as wrong.
Next changes are in the backrow, where Sean O'Brien comes in at 7, and Toby Faletau replaces Jamie Heaslip at 8. This are two stupid calls. First off, Sean O'Brien is not a 7. His ball carrying and his presence means he should be there, but at blindside. He is decent at the breakdown, but decent won't be good enough against George Smith. Especially with no help given that Heaslip, O'Driscoll, Rory Best and Dan Cole are not selected, their replacements don't effect the breakdown at all. Furthermore, Healy and O'Connell aren't around to help O'Brien, who will be massacred. Tipuric should be starting, and ably assisted by O'Brien from 6, and Heaslip from 8.
Phillips to come back in at scrumhalf wouldn't usually be a bad decision, except that he is out of form and short of fitness. Green tinted glasses on, Conor Murray has been the form scrumhalf, and that is reflected in his selection on the bench ahead of Youngs. Does Philips deserve to be there?
Gatland's excuse for dropping O'Driscoll was that Roberts gives more. But O'Driscoll isn't being replaced by Roberts, as Roberts is playing 12. Jon Davies is lucky to be in the squad. As the third best outside centre in the squad, how Gatland can justify his selection over Manu Tuilagi, never mind O'Driscoll is beyond me. See below for Davies's qualities.
Finally, for the captain, Gatland has made another clanger. Alun Wyn Jones has only captained Wales once. For a new captain to come into one of the biggest games in rugby is bizzare. Just ask Jamie Heaslip how difficult it is. He is usually a fired up player, and as Paul O'Connell knows, dealing with Romain Poite as fired up as Alun Wyn gets is going to be nigh on impossible.
The Lions could still snatch this, but with no help at the breakdown, it won't matter who the centres are, they will get less ball than last week. Gatland you've gotten this wrong.