I've played all of my games solo, since I need to play them a lot more time than I can get enough players together. But I think there are better solo games, since the amount of secret info makes playing solo less awesome.
I will say that among my designs, the most fun 'solo' experience would be using WW2 QMG with both expansions and the optional deck construction rules. This allows you to try out some really unusual strategies, perhaps just varying one deck at a time.
I have thought about publishing some optional solo rules for the games, which would include putting 1-3 cards from hand to the bottom of your draw deck each turn and then not looking at your cards during the draw step.