Lag is always an issue in games, but some games it's much worse than others. The developers behind the FPS games Tannenberg and Verdun have made some steps to improve this.
Super Indie Karts from developer One Legged Seagull is actually quite an impressive retro-inspired racing game. The latest update adds in a 25cc mode, which is better for beginners and younger gamers.
Introversion Software have updated Prison Architect once again! Update 16 that's currently in Beta adds in cooperative prison building for up to 8 people.
The Universim, a hybrid of a god game and a city builder launched into Early Access recently, although it was missing a file for Linux users which has been fixed.
How do you know Linux is gaining steam outside of the usual circles? When you see writers like Jason Evangelho from Forbes switching over to Linux and writing about his experience.
Developer Turtle Juice might have made the most insane game I've seen for quite some time. Fluffy Horde is a 2D side-scrolling hybrid between real-time strategy and tower defense coming to Linux.