What strategy/simulation based games would I love?

Total Annihilation has been re-implemented in a more modern 3D engine, http://spring.clan-sy.com/. It has slightly higher requirements than the original engine but is still well within the envelope of any machine built in the last decade. Even runs on Linux. Dwarf Fortress flew to mind reading this question. There was a great post on mefi about it http://www.metafilter.com/63759/All-go-no-show.

If you're a sports fan, one of the best is the online soccer management game http://www.hattrick.org/. I'm not even a particular football fan and I was quite absorbed for a few years ...

I'd like to third the mention of http://www.battlefront.com/products/cmak/cmak_bundle.html. It's got a great order system (both players submit moves and they're resolved simultaneously in real time). It's super fun to set up your orders and see how they roll out. Some of my favorite moments are attaching my view to the back of a tank that's hightailing it across an open field under fire. The graphics aren't great, but they're evocative. Its modeling of command delays, morale, armor penetration, movement, etc are both fun and convincing. Also: watching artillery fire come in (3 minutes after you called for it, so you have to plan ahead) is pretty spectacular. You also get a pretty great sense of the different tank types. Other games have the tradeoffs broadly right (Panzers tended to be slower, better armored, and with stronger guns, American tanks were faster, more numerous, usually had gyro-stabilized turrets), it's a totally different experience when you actually use individual tanks on the field.

I agree with the recommendations for Dwarf Fortress and Imperialism 2.... well, honestly, most of the recommendations here that I'm familiar with are very good. But I know DF and Imp2, and I'll bet you'd like both a lot. One that I've never personally gotten too enamored with, but which I know has a real cult following, is http://www.hollywood-mogul.com/, a text-based movie studio simulation game. It's quite intricate. I lost interest when I realized I needed to be keeping notes to play the game properly; with computers being as powerful as they are these days, I figure a game that needs note-taking has an interface problem. But if needing a paper notepad doesn't annoy you, HM might be right up your alley.

It isn't that rules intensive, but if you want a neat and fairly fast game to play I've been playing protector. http://www.kongregate.com/games/undefined/protector It seems like it is strategy light, but there is a correct balance you need to find with putting your guys too close to the front and leveling them up too fast so that the people towards the end don't get any experience. Plus it is a web game so it is free, a small download, adn availible on any platform as long as it supports flash.

Another shout for Dwarf Fortress. It should be right up your alley.

Second the Paradox Interactive games: Europa Universalis II; Hearts of Iron II (which makes HoI I redundant); Victoria Revolutions; etc. Hearts of Iron II has a 100+ page manual that is required reading, so that's up your alley. Also seconding Combat Mission II: Barbarossa to Berlin. Also, consider the games being released by relatively new developer http://www.ageod.com/. And maybe what you want is full-on bearded-gamer wargaming, in which case http://www.wargamer.com/Default.asp is the review site you should check out.

I'm playing http://voximperium.com, free, online, real-time strategy. I don't know that it's quite got a cult following as such, but it could get there. Games can last between four hours and a couple of months depending on the way they're set up, graphics are basic, documentation is likewise - but if you read your way through the forums you can find a lot of explanations and tips that aren't in the official instructions.

http://www.everybody-dies.com/ is a global nuclear war simulator that's light on the graphics, and definitely has a cult following. Available for PC/Mac.