Factorio is the most successful game on steam. It has no singleplayer campaign either... they're just adding it now.

Just be transparent about where you are and what your plans are.

Go greenlight. They Are Billions launched early access without a campaign and did just fine. Same for The Long Dark. Wreckfest was notorious for it's long early access cycle (years!), but turned out fine.

I'd happily chuck $10 at something like this.

Why not make it Early Access (if you're actually planning on releasing a fully fleshed out singleplayer campaign), brand it as a sandbox game and be clear about what's working and what's not yet implemented? I would buy this game based just on the info you put on the website :)

Personally I was really surprised it was free. It doesn’t have a lot of content yet but what it does have is great.

That said, it may be hard to switch now without garnering those negative reviews you are talking about.

I'd buy it right now if I could. I got hooked instantly and only slept 4 hours last night as a consequence, I'm sitting at work thinking how I can fix my build. It's seriously decent enough for an early access title, all it needs is more fleshing out for the campaign and some UX improvements on the menus.

I was literally ready to pay for it right now and then i saw it was free.