WHAT THE GOLF? is still getting free upgrades and the latest A HOLE NEW WORLD Update is live with another bunch of levels to play not-Golf through. See also: some previous thoughts.
The actual release announcement on it is pretty small that doesn't really go into any specifics. What it gives is a few new official levels to play through in a new adventure. The key feature seems to be holes, and a lot of them. You're not just avoiding static holes - oh no, there's plenty of holes that move, shrink and grow and you even become a hole yourself and attempt to swallow the flag in one level.
Triband continue to impress with how they've able to throw out every single possible rule in Golf, and make a ridiculous and thoroughly entertaining game out of it. One level even has you attempt to eat everything on the screen, to grow a hole big enough to swallow a house - what other game can you say does something like that? It also features plenty of their very silly but enjoyable puns each time you complete a level.
With this new content you're probably looking at an additional 1-2 hours playtime, depending on how difficult you find the new holes.
It continues to be an easy recommendation to go and buy.
You can buy WHAT THE GOLF? for Linux on Steam.