I love this mode. It has amazing potential... The only thing missing is content. I understand this is new (and the game itself is new as well) but I feel like without more content, there isn't much to do. I recognize that Garry's Mod had years and years of building from modders behind the scenes, but there needs to be something done to allow more content whether it's original content, or ported content from other games that is easy to implement for coders and non-coders alike.
An in-game Weapon/NPC/Behavior creator is MUCH NEEDED. Upload your model, quick rig, set behaviors (preferably with tempaltes available) would add so much more content in such a short amount of time.
Additionally, if possible, adding more mountable games would help in the meantime I believe!