Yes, even though Nintendo has had a hard time recently with the failure of the Wii U and a lack of new games, it is still very popular and has many dedicated fans. With Pokemon Go, the announcement of the mini NES Classic Edition, and the NX coming very soon, Nintendo has a lot more popularity in its future.
The hayday of Nintendo was the eighties and nineties. People who claim themselves as "nineties kids" share fond memories of playing different Nintendo games. Now, though, the market is over-saturated and the interest that people used to have in Nintendo is waning as exciting new videogames come out and people feel compelled to play those instead.
The two most recent consoles, Wii, and Wii U did not fare nearly as well as the most recent Xbox and PlayStation consoles. Older consoles, games, and characters are still popular, but not at the level that they once were. Nintendo is no longer the leader in gaming that it was.
No, Nintendo is not as popular as it used to be. That is not to say that it is becoming unpopular. Rather, it is simply not the only "game in town" anymore. In previous decades, if a person was into videogames, they really only had a couple of choices, namely Nintendo and Sega. In this day and age, gamers have a much wider variety of options, many of which are available as free apps that can be downloaded right to their smartphone. It is no longer necessary to spend large amounts of money on a system that can only play a certain amount of games. So, Nintendo is undoubtedly still popular with some, but not all.