Nostalgia!

I'm feeling so nostalgic right now! The memories of my favorite computer game, Gothic II, are really hitting me hard. I don't even know what to do with this feeling, and I can't even play it right now – my Windows installation is messed up, so I can only use my mobile device to browse the internet. I'm feeling so nostalgic that I decided to write about it in this section.
To make this thread a bit more meaningful, here's a question: what games do you constantly feel nostalgic about, or what games are you feeling nostalgic about right now? Ideally, with some explanations (not like I did :) ).