i don't knokw if Unity is a good choice (even considering you could make GNU/Linux and OSX builds too), i think Unity is too bloated, specially for this kind of game - maybe Python-Pygame, Lua-Löve, etc., would be better?
I'd go for Unity as I'm pretty fluent in it and could use the Adventure Creator plugin to port it in a weekend. I'm far too deep into programming in C style languages, that I've never been comfortable in Python or Lua.
