The file is a RAR, you need to extract it to access the game.
Not having any issues whatsoever over here. It shouldn't really make any difference afaik, but I used 7-Zip for extracting the files.
The game starts up and seems to play without any issues as well - although I can't claim to have progressed particularly far, nor am I in any rush to, as I was really just planning on letting this one sit and grow in content before giving it a real try. But I saw this discussion and figured I'd see what's up, so here we are.