Proteus is wonderful. So wonderful it needs more space, variability, events, structures, animals, plants, time, music, feedback, etc.
Antichamber was more fun to play as a demo a couple of years ago. It went from purely logic puzzles to mostly cumbersome block puzzles, though the start still maintains the heavy use of proverbs+insight. Certainly a clever game, but its nonlinearity and lack of a decent navigation system cause unnecessary meandering and jerky progression. Visuals are just good enough.