In your opinion, does the 5E Ranger have its own thing? If so, what is it? If not, what should it be?
Kind of? The D&D ranger is a
monster hunter. Both in that it hunts with monsters (beastmaster) and it hunts other monsters. There's room for a Blue Mage style use of monster powers. Tracking is an important part of a Ranger, since hunting involves a focus on tracking prey, but its not the whole of the hunting stick.
While others may say that "hunting" can be shared with anyone? Fighting can be shared with anyone, and yet we have the Fighter class. Sneaking and backstabbing can be done by anyone, and yet Rogue. Its strong of a niche.
The current problem isn't that Ranger doesn't have its own stick, its that the 5e mechanics are kinda crappy for reflecting it. The Beastmaster is a mess, TWF is a poor option when its supposed to be good at it, Hunter's Mark is terrible for a primarily melee build, too many tracking options when people are happy with a WIS check, better ways of handling stealth (yes, the Ranger is just as much of a stealthy class as the rogue), environmental/favored terrain issues, spell and bladework don't synergize well like it does with the paladin, the magic is still described as "druid lite" instead of its own. There's likely more.
The problem isn't that the Ranger doesn't have a niche. The problem is that the Ranger has no idea how to translate its niche into D&D. Part of this is the rule system - unlike the robust combat system, both the Social and Exploration pillars just use simple skill checks. Expertise, perhaps with someone granting Help, covers pretty much anything you absolutely need to pull off most tracking situations. If we had more robust exploration rules, we'd see more people drooling over the ranger, I think. Part of it is that there's a need to be distinct from the Fighter and Rogue, and no real known way to pull that off in combat. Part of it is the need to get over the idea of Aragorn and the 1e Ranger. Modern rangers don't want, or need, to act like a Fighter, as the 1e and 2e versions did.