The slow pace at the start, and the somewhat lifeless 2D isometric graphics simply didn't do it for me.
But the blog posts were fascinating, and people kept raving about it, so on that 4th install I decided to soldier on and actually get somewhere.
I now rate it as one of the greatest games ever made. It is insanely technically impressive, able to run megabases with trains and belts and robots and inserters and all the rest of it at 60 FPS. It doesn't crash. It's incredibly fun and very addictive. Amazing mods, amazing community.
I can't wait for the expansion. I'll just assume from the start it will be as polished as Factorio is.