There's still Age of Mythology: Extended Edition and Impossible Creatures Steam Edition if you want some classics.
As for newer RTS games, I have been enjoying the hell out of Divinity: Dragon Commander, which is a combination of Grand Strategy (turn-based) and RTS. The biggest disadvantage there is that the multiplayer section of the game is almost permanently abandoned, so you'll have to make do with the single player campaign. On the positive side though, the single player campaign is fantastic, and really worth playing. Get it in a sale or something if you care, it's pretty much a hidden gem.
Another RTS game I can recommend is Offworld Trading Company. It's more of a trading and resource management game in which you try to disrupt and sabotage your opponents to make maximum moneys, on Mars. It's not about building an empire and fighting people with armies, this is about claiming resource-rich territory, building extraction facilities, boobytrapping enemy facilities and trade convoys, researching tech, manipulating the market and buying out the other companies. Has a lot of freedom and custom map creation, and can get more tense and exciting than it sounds. I wholeheartedly recommend it, it's very cool.
(As we speak, Offworld Trading Company is at 50% off, which makes its price very reasonable)
Otherwise I can recommend games like Civ Beyond Earth, Civ V, Endless Legend, etc. but those are mostly 4X games, turn-based rather than real-time, and maybe that's not what you're looking for.