Factorio Forums

Gimbal
If you aren't familiar, it's a build spaceships and make them fight each other game. It's a great concept, but the dev(s) aren't active and so it suffers due to people exploiting flaws in multiplayer, a lack of players in general, lack of support and updates, etc. If it had people like the Factorio devs behind it, it could be amazing. But in any case, it's fun, and for people like Factorio players, it's a pretty natural fit.
URL: http://gimbalgame.com

Symphony
This isn't at all Factorio-like, but I like Symphony pretty well. I've got lots of Symphony vids on youtube if anyone wants to see advanced-level gameplay. Not to toot my own horn, or whatever as I'm sure anyone who really tried could beat my runs, but most youtube Symphony vids are absolute amateur stuff.
A couple of my vids:
https://youtu.be/yfKjUETXXCg
https://youtu.be/u3RYeT6dvZE
https://youtu.be/RisL1lYsZVY
Game URL: http://www.symphonygame.com

Scrap Mechanic is a physics-based game that's like...if you started at Factorio, and walked straight to Minecraft, then kept walking in the same direction for about the same amount of time, you'd end up at Scrap Mechanic. It's 3-d-ier, physicsier, laggier, less logisticky, and WAY more contraptionistical.

So I've been playing a few smaller games, waiting on 0.13...

First KeeperRL
Really cool dungeon building game. Still Alpha, but I spent several hours playing it.
Definitely get it if it's on a special.

Then Creeper World III
Really a lot of fun! Very additive. Again well worth the bay if you get it on a special.

I was going to say I also play Symphony of the Night, but then I realise you were talking about a different game.
I'll be playing Salt and Sanctuary when my thumb fracture heals (2d platformer version of dark souls with some very limited metroidvania elements).

I was playing overwatch with friends until I got hooked on factorio a couple of weeks ago and haven't played any other games since.

In general I like open world games. Being able to build an empire is a bonus. So Civ, Mount and Blade, X3, Terraria, Minecraft and also some Rise of Nations which is an RTS version of Civ, though the multiplayer is quite dead/toxic on steam and has either total noobs or elitists (and frequent dc/sync issues), though the gameplay is quite good.