I honestly don't mind the sunglasses so much. Every Doctor has their goofy things: 2 had his flute, 4 had his jelly babies, 5 had his celery, 7 had his umbrella and spoons, 11 had his fez, etc. The one thing that is a bummer for me is that I had hoped that the opener meant that he would have no sonic at all for a while. I don't think the Doctor should always have his sonic - he used it rarely (and mostly for small things) in the classic series, and it was definitely overused by 9, 10 and 11 to get out of some plot problems a bit easier. It became more of a magic wand than a screwdriver (I mentally high-fived myself when John Hurt gave Tennant and Smith some shit when they tried to act like their screwdrivers were actual weapons in Day of the Doctor). Basically it created the same problem as when K9 became a constant companion for the 4th Doctor for a while. I love both the screwdriver and K9, but I think less is more.
If this Doctor is going to have a sonic, I don't particularly care that it's a pair of sunglasses. It's goofy, it's so uncool that it's cool again, and it fits his semi-retired 60s rocker style. After all, the original joke with the screwdriver was that a screwdriver is the lamest, most uncool weapon the Doctor could have, and that made it cool. The sunglasses work with that, I think. I think it would have been cool to have a Doctor that wouldn't use his sonic at all for a while, but eh.
Also the sunglasses have the potential to create some very fun moments. I loved the look of the Doctor wearing them while looking through the porthole at those ghosts, for instance.
