I've only been there once in 10 years, but if you pick the right day (waiting for low humidity is key) it's incredible. Our views beat any postcards that we've been able to find (my pic below). We could see Alsace and the Black Forest. Plus the train journey through the mountain is amazing.
I agree with Treverus and FunnyBone that to a certain extent it's simply on the "list of places to see and take a selfie" for many tourists, hence the popularity. I do think that the experience itself is worth doing at least once. Whereas e.g. the Eiffel Tower, Jet d'Eau in Geneva are famous because... well... they're old, famous, sort-of-impressive things, the Jungfraujochbahn journey and scenery is properly