Google Earth VR is my recommendation to people just trying out VR for the first time. It's pretty much exactly what you'd expect, but somehow seeing where you grew up, or went to college, or whatever is just a great first experience for a lot of people.
Beyond that, there's an entire category of "Travel the World" apps out there. I'm a big fan of the Ocean ones, but look around in the category to see what sparks interest.
YouTube is also a great source of videos. I'm a fan of the "360 Walking Tours" of various cities. Even the ones of the city I live in are great, though I gravitate to the big bright cities like Tokyo and Hong Kong. And of course, there are plenty of more fast paced videos, like 360 videos from the Thunderbirds and Blue Angels that are pretty fun. Some performers are also have concerts (or even do live concerts) in 360 if that's your thing.
Beyond that, don't rule out the games. Aircar VR technically has goals, but it doesn't enforce them, and it's great fun to fly around a Blade Runner inspired world. Beyond that, some of the story games are really good. Ghost Giant is a fairly easy puzzle game, and while the story was a little saccharin for my tastes, it was really well done and fun.
Beyond that, a lot of my friends seem to love the Theater apps like BigScreen. This has never really worked for me, perhaps because I don't have lots of great memories of theaters for whatever reasons, but for those missing that side of life, it seems to be a good option. I got more out of the social side of that, but only when using it with friends, when entering the public rooms, it's too hit-or-miss if you get a griefer or not for my tastes.
And of course, I think there's a law that every VR owner tries out Beat Saber. I really like it, but beyond that, it's a great app to show off to friends, since it's trivial to get started in.
Of course, don't take my word for any of these, I recommend you dig into reviews and see what floats your boat.