Tempted to buy this but I'm not sure it's worth it for only playing solo?

I played through solo with no issues. For all intents and purposes it is just fine solo. There are only a few community maps that are coop only.

great game solo

As someone who has been steadily knocking his way through the official rooms solo, this game is great for solo players. In fact, a few of the rooms have segments seemingly designed with solo play in mind. (EDIT: Apparently some of the official rooms, especially the newer ones, change slightly when played in co-op to accommodate team-based puzzle-solving. So it seems like my assessment was accurate, but not for the reasons I expected!)

It's pretty cool within the workshop, but I recommend playing with friends the official maps