I think I know what they mean, if you look at the other game they have put a lot of work in those 6 or so maps. What I did was work smart, and I created a procedural way of creating maps (because I'm lazy.. aren't we all?) and it doesn't look as appealing.
But now I'm gonna take a different approach from now on. Still creating those procedural maps, but now I'm also creating some special ones based on real life mini-golf courses (powered by google images). This is (I hope) what they mean by lack of polish. For me as a programmer, all I care is the gameplay and the fields (where the ball rolls), the rest is secondary, but for the average player graphics and pretty stuff is always more appealing than the game core mechanics.
Still, this is a path, project is not dead, and like I said to them I'll keep improving.
PS: They replied saying they are willing to change their review (and they even said they didn't want to give a bad review, just a neutral from where the game stands TODAY). So I'll just work until they change their minds, and make the game better in the process.
Meanwhile I'm also writing a post-mortem that is 7 pages long so far, and still isn't done. This post-mortem is probably the most detailed post-mortem out there (or one of them) since it's basically a tutorial on how to get on steam, and the do's and donts from my point of view (just my opinion).