Simulation games is a broad brushstroke and, frankly, you could argue the case for most games to be some type of simulation.
With that in mind, my two favourites are Rule The Waves 2 - research, design and build a navy, persuade the politicians to give you the budget and clean up their mess when they start a war. It's probably best described as the Championship Manager of naval games.
Rule The Waves 3 releases this month and it will be a 'just shut up and take my money' moment for me when it does.
My second one is Shadow Empire - 4X planetary conquest at its very best and probably the most complicated 4X game I've ever come across. Highly addictive and very replayable. It takes months to master and can be frustrating but it's all worth it in the end.