There had long been rumours that this would happen - but then, there were lots of rumours about Obi-Wan and Anakin too - but it's still a wonderful surprise to see Yoda's Force Ghost return to the saga.
He's considered the wisest of the Jedi, and he appears just when Luke needs some sage advice the most - except, of course, it doesn't go at all how Luke expects. It's another subversion, with Yoda dismissing the ancient Jedi texts, and there's an immediate reconnection of their relationship that's simply a joy to watch. It's funny, poignant, and entirely necessary for Luke's story to advance.
How would you rank the characters of The Last Jedi? Let us know down in the comments.