The short: pleasantly surprised. Rust is the foundation for something greater. Will the devs manage to craft it?
The long: you’d have to be blind to not see the huge potential this game already has. Just by introducing farming and a trading system, you could support whole towns filled with people. The players would then create their own currency systems, and trade goods as well as services. Towns would develop their own laws, and expel or execute repeat offenders. The game should have a weather system, so that droughts (and natural disasters, such as fires, and possibly diseases) and the ensuing famine would stress a town’s cohesion to a possible breaking point, causing chaos and mayhem that would prevent the game from becoming stale. Lawlessness would certainly be rife: you’d have gangs, contract killers (I want you to kill cellcore and burn his house; he’s about 6 foot tall, usually goes around naked and has a normal penis), racketeers (pay us a certain amount every day, or your house goes boom), corrupt officials, etc., and law enforcers to put a stop to them.
Basically, a game with a solid framework (crafting, trading) and a source of entropy (natural disasters, PvP) that would allow the players to make the game what they want it to be.
Alternatively, you could have a game where you build a fort and kill anyone that approaches it. Over and over again. For several months. Without somehow getting bored.