It had a good run, and even today there are folks who strongly prefer Windows Phone 8.1 to Windows 10 Mobile. However, you cannot deny that it will no longer be supported by Microsoft.
But is it still worth using for some people? That's the topic of a new discussion in the Windows Central Forums.
On one hand, if something still works great for you, it still works great for you. It isn't being supported anymore, but if your needs are fairly minimal maybe you'll be just fine. Especially if in your case upgrading would mean getting a new phone. Not everyone can or wants to fork out for a new device.
However, the Windows Central team is pretty unanimous in its approval of Windows 10 over Windows Phone 8.1. It's far from perfect, but it's the best it's ever been.
That's our opinion. Be sure to share yours in the forums thread linked below.