3-D was kinda introduced because too many people were waiting for the films to hit DVD and legal phone downloads... because, you know... it's every director's intent to have their creation viewed on something smaller than a postcard.
It worked initially, Avatar made a crapload of money (mainly due to 3-D sales), and the 3-D sales pushed box office sales up. Then they got hubris, and raised the prices and made every film 3-D. And now,
everything has to be 3-D. I remember when the term Hi-Def was used on
sunglasses. They were no different than any other Sunglasses. Same thing here.
3-D works on some films, on others, it's just blurry and fuzzy and distracting. Though, there
are films I really regretted not seeing in 3-D, some of the live action ones I've seen I'd give or take that. It was pretty good in parts of Avengers, it was hardly noticeable in other scenes.