Everything is a good photo opportunity, but not necessarily for every photographer, depending on their style, their equipment, their knowledge, and the time they have.

There are a lot of things about Christmas that annoy me, like the Christmas markets and the hordes of people they bring when I usually try to avoid photos of people. But Christmas lights are not much of a problem to me. I see them as part of an ongoing transformation of a city. Cities evolve around the seasons, they change as buildings are built, demolished, rebuilt, renovated, they change with festivities, etc. If I am photographing in my local area and think I don't like the Christmas lights here, I could save my current position and remind myself to come back here in January. And if I am traveling, well, I try to make the best of my time there. If I traveled specifically for photography, I would be timing my trip depending on what conditions I want in the city, so I wouldn't have any issues.

And on the technical side of things, Christmas lights are no more of an issue than any other artificial light source. Night photography really requires you to know your gear well, know how to use manual or semi-automatic modes, and know how to use post processing software, so it certainly is more complicated than daytime photography, but it can be very interesting. It also gives you good arguments when someone says you could just take photos with a smartphone.