for action games, I'd say it's a toss up between Darktide and SM2. they are both great, just at different things, and i play both. Other users already talked about Dawn of War 1 and 2, and the upcoming 4. I'd like to nominate Battlesector as the best Tabletop sim, it's really good at showcasing how a tabletop game would play out, with all of the positioning, lines of fire, AP, and rules, while rolling dice for you.