I pound it into students' heads that games must either be completely self-explanatory or provide tutorials; dumping the player in at the deep end to sink or swim belongs to the arcade days and is no longer acceptable.
Some time ago someone suggested that I play Crusader Kings II because I'm interested in diplomacy games. It is currently my second-most-egregious example of how NOT to introduce a player to a new game.
(My most egregious example is a master's student project from an institution that will remain nameless, which puts the player in an environment with no HUD and no explanation of who she is, where she is, why she's there, what she can do, what to do next, or even what the controls are.)
Crusader Kings II is the opposite, overwhelming you with vast amounts of minutiae, huge numbers of icons, and long hint text that doesn't tell you what to actually DO or how to do it. There's a tutorial, but it was clearly written by someone with little capacity for putting himself in the player's shoes.
I'm sure I'll get there in the end. I want to like this game. But right now it feels like being handed the keys to the space shuttle and told to take off.