Hands down Little Big Adventure 2. I adore this game, it's one of my all-time favourites. LBA2 eventually made me fascinated with games. It surely represent the French Touch ones of that era. Games that were gentle yet engaging, fun and smart. The first area - Citadel Island - was a quite amusing open world location where you could check every corner, run around and interact with new NPCs - talk to them our just punch them without any particular reason. And all of that in 3D, I remind you. The soundtrack was just the cherry on the top. Hits me right in nostalgia every time. I strongly recommend everyone to check this game. It's available on GOG.com and is sure worth the money.
Twinsen's Odyssey is the reason I opened this thread. The music has stayed with me many years later, something few other games have accomplished. It was so strange and unique and addictive. It would be interesting to see that franchise get rebooted...