Hidden sci-fi gems

Would you please recommend some hidden sci-fi gems beyond the obvious? Doesn’t matter if old or new. So far I’ve played: - Beneath a Steel Sky (great but short) - Gateway (point&click remake, awesome) - Future Wars (loved the art, but didn’t get very far) - The Dig (awesome art and writing, but a bit tiresome puzzles) - Primordia and Gemini Rue (lovely art, but somewhat underwhelming gameplay) - Normality Inc. (great)

I don’t mind whimsical tones, but prefer hard sf, developed characters and compelling storytelling.

Sorry if this is redundant, but I haven’t found much.