This question makes me think. Do you consider OpenTK well-documented? What parts do you consider lacking? What would you like to see?
I don't really know where OpenTK is standing in the documentation issue. According to Ohloh, 30% of all source code lines are comments, which is higher than average (22%). Considering OpenTK contains around 850000 lines of code, this number is nothing to laugh at. (Yeah, the numbers are probably overblown, no I have no idea how they are calculated :-).)
OpenTK is built on the premise that you are using an IDE with code-completion and documentation tooltips. Used on its own, it is actually more complex than straight OpenGL or OpenAL. This additional complexity is spent on type-safety and function overloads that smooth the differences between .Net and native code, which is a major win when using a .Net IDE like Visual Studio, MonoDevelop or SharpDevelop.
Is OpenTK usable without an IDE? Certainly, but the experience will not be as smooth. Strongly-typed parameters and function overloads won't help if you cannot discover them in the first place. So if gedit and make are your cup of tea then OpenTK might not be the optimal choice (but do check whether your editor supports .Net code completion - many do!)
Of course this doesn't say anything about the quality or usefulness of the documentation, so if you have any thoughts or suggestions I'd love to hear them.