I have played to level 40 last night. I have some thoughts. First, I consider the market fairly cheaty for gaining levels - once you have the sales price upgrades and the selling = xp upgrade you can buy and then sell high value items every 5 minutes, times however many markets you care to build at only a slight loss on some items, and a gain on yet others such that you can gain XP very quickly and gold at a slower pace but still positive. Since this is scalable, I view it as an exploit. Gems appear in stacks of 30 or so in market. Keys appear in stacks of 20 or so in market. I think their appearance is level dependent not just getting the "stores have gems" upgrade. In any case, keys are 40 regularly and gems 60, and can be sold for about the same. With several markets I can level up every 5 minutes provided I had a good stack of gold (like 5-10k) to start with. This is vastly superior to any other XP gain method I have found so I am going to say probably an exploit vs. intended balance.
When selling 30-60 gems or 40+ keys, the resulting stack of gold is extremely laggy until I pick it up. No crash yet from this however I'd recommend as others have to spit out a 10 or 100x coin object when selling if the sale exceeds the amount, as lag prevention.
I do see lag from the world as it grows, if not picking up items constantly from the mines. Some method of picking them up from mining automatically, perhaps into a chest or something, would reduce that problem, or consolidating items into stacks.
Another thing I noticed is the ability to walk inside building tiles that are on top of rafts, meaning the building is partially solid.
Rafts and roads can be spawned mid-block, but should probably snap to the closest tile visually. I haven't figured out what the function of the roads is, but I was going to test if I can stop resource spawning with them everywhere except a couple of areas where I want to concentrate the spawns for mining.
Finally, if you plan to implement the combat, a pause feature is essential. Right now only going to skills seems to pause the processing. Toggling with say "P" is an easy way to do that. I did notice you don't consume energy when not moving or performing actions so in the current mode it's less of an issue to AFK.
Also, would like it to not reset my zoom level every time I interact with buildings.