The Witcher 3 got its first major expansion last week in the form of Hearts of Stone, and I thought it was pretty good. Since then CD Projekt RED has acknowledged and promised to address a series of issues ushered in by the new DLC, and that's about to arrive with patch 1.11.
It's a huge list of minor changes and tweaks, so if you want an exhaustive overview you best click over here. Among the highlights are rebalanced boss battles – basically, the challenge they present will more closely mirror the difficulty level you're playing at.
The patch applies to the main game too, so even if you don't have the Hearts of Stone DLC you may notice some improvements, and a couple of bugged quests have been patched over as well.