Just about every full frame digital camera ever made is still worth using to this day. There are a few exceptions, the original Leica M8 was more or less a steaming pile of garbage. It had a host of dealbreaking problems, from exposure inconsistency, UV sensitivity, color rendition, to a very slow and clunky UI. It was an insult to buyers of a $5500 (in 2006 dollars) digital camera that bore the Leica name and could mount some of the greatest 35mm glass in the world. Fortunately, the M8 is an exception. Most full frame digital cameras (SLR or otherwise) are still a blast to use. Even older cropped sensor cameras with swappable glass are still good for subjects that are far away.
I have an OG Canon 5D (that is, ahem, IR modified) that I am going to dig out, clean off and fire up this spring. 12MP is still plenty for my purposes and a full frame sensor plus a wide zoom (in my case 17-40mm) is just too much fun.
Unedited photo, straight out of the camera.
Fussed over in Photoshop.
Meow.