Personally, what really makes a good NPE for me is voice-acting.
I don’t like having tons of pop-ups everywhere, but a voiced tutorial that is tuned correctly, that works better. I don’t wanna spend time reading in a video-game!
If there is no voice-acting, then it needs pictures. World of Warcraft (which is free up to level 20 by the way wink wink nudge nudge) has an awesome early-game tutorial experience to teach you the basics. It fails at some advanced things like using the chat, but in general, it’s pretty good. Even has an NPC with voice-lines teaching you about the basic skills of your class.
That’s more of the kind of things a game like Boundless needs, I think.