I don't think we know actual problems they solve better than classical computers. In many senses, they "feel" like analog computers, which had niche applications for quite some time before good enough digital computers outperformed and replaced them. Where they seem more promising is at simulating quantum chemistry problems (which is what Richard Feynman imagined them doing well before the first one was demonstrated).

I sat down a couple weeks ago with some experts and what I got is that some key parts that make a general purpose computer as we know them today are missing (bear with me - I'm a total newbie on this), one that struck me is quantum memory, because we just can't really store anything for a significant time in a way that we would be able to input the result of a previous computation into a new one. Also, the notion of a stored program (in memory) is very alien to quantum computers just yet.

That said, D-Wave says they are solving real-world optimization problems on their not quite general quantum computers, so I won't dispute that.