I played the solo game last night (this was the first time I played the game). I was just planning to play once, but I ended up playing four times in a row. It's a fun puzzle, and trying to beat your best score is surprisingly compelling. (I scored the same in my first three games and was afraid I'd reached a ceiling; in my fourth game, I beat that score by four points.)
My assessment: Colony is a fun solo diversion. I probably wouldn't buy it just for solo play, but it works well for the purpose if you've already got the game for multiplayer. (I've not played multiplayer, but I'm looking forward to it.)
What was your score?
I tried solo twice at a con over the weekend; first game I was doing so terribly I just quit and restart. Second one I felt like I did well but I only ended up with 10 points.