Oddly enough there was no thread.
Anyway, the expansion hit in the past week, where you play as Plague Knight. The timeline runs concurrently with Shovel Knight's, and you actually almost cross paths (reminiscent of the SA-X encounters in Metroid Fusion) throughout the story. The mechanics are quite different, as you'd expect. It makes the game easier in some areas, more difficult in others. Your main attack is throwing bombs, which you can upgrade in three ways. The upgrades are plentiful and it's fun to try out the different combinations. You also get a charge "bomb jump" that is necessary for passage through most levels. This is where I've had some trouble. Whereas Shovel Knight's controls are pretty fluid, I've had trouble nailing down the bomb jump. Mainly because your control is very limited once its engaged. I've jumped into pits accidentally numerous times, and it adds frustration in areas.
Aside from those hiccups it has been fun so-far. It's nice to have more Shovel Knight to play. And the change in mechanics work to make the old areas seem new again. Also, it's free. So if you have purchased Shovel Knight you have access to it.