tpholt, now that you've discovered Zulus on the Ramparts, you're at the brink of some really awesome games. It gets way way better than Zulus!
I think Robinson Crusoe is a mess, but it's gotten an expansion and maybe a second edition. I presume some of the issues have been straightened out.
The trick with solitaire gaming is finding a) a game built from the ground up for solitaire rather than a multiplayer game with some half-assed bot scripting, and b) something that fits the level of commitment and detail you want. Going backwards through this thread should offer you plenty of suggestions. Also, keep in mind that 90% of "co-op" games are actually solitaire games!
One problem for me is that I don't have a lot of patience with the typical solitaire AI of just throwing a flood at the player and tasking him with holding it back using limited actions. Pandemic is godawful for so many reasons, but mainly for this. It's like rolling a four-sided die against a six-sided die and trying to accumulate a higher number. Ugh. This is how the various states of siege games work, which you saw in Zulus on the Ramparts, but they have a wide range of styles that adapt to the idea that you've got a d4 worth of actions to hold back a d6 worth of enemies. I love Ottoman Sunset for its historical strokes and simplicity. It's about on the level of Zulus at the Ramparts. The zombie theming in Dawn of the Zeds is unparalleled, but it's super detailed, having been designed by a guy who makes wargames.
If you're into heavy games, you have a lot of options. You're probably right to avoid Comancheria, which is really detailed and it requires a serious commitment to learn. It's got a unique approach to AI, but if the subject matter doesn't work for you, it's probably not worth the time it takes to invest.
There are, of course, plenty of good solitaire wargames, but you have to be into wargames. An epic sci-fi game called Struggle for the Galactic Empire is a bit, well, abstract given the scale (each turn is a generation, each space is something like 10,000 light years, and each chit is a massive fleet of thousands of ships), but it's also got a cool AI system. The abstraction gives it some nifty ways to play with things like alien invasions, rebellious systems, and political intrigue.
Fantasy Flight's Lovecraft boondoggle, Eldritch Horror, isn't heavy so much as finicky. I like it a lot as a game about flipping cards and making your own adventure/horror movie. The Aliens Legendary game is another cool card-based approach to making your own adventure/horror movie with a set of cards for each of the four movies. Dan Verssen does a bunch of solitaire games called the Leader series. They're really good as military hardware porn/campaign games. Hornet Leader is probably my favorite. Steer clear of his Warfighter games, which are a mess built around selling expansion packs. Shadi Torbey's Oniverse games, published by Z-Man, are all excellent and I wouldn't hesitate to recommend them to anyone; they're lightweight and playable in short slices of time, but they're so approachable and enthusiastic and charming, and they fold in lots of nifty gameplay variations as you ramp up to playing the full game. Start with Onirim.
If you want to find out more, you can read reviews of a lot of these on the front page. I'm sure I'm forgetting a bunch, too.