Halo Wars 2 stands as my favorite RTS. It isn't very complex, it's easy to learn, fast-paced, fun, additive and full of content. A decent main campaign, an enjoyable side campaign (Operation: Spearbreaker) and a good campaign involving a familiar disgusting foe AND playing as the Banished (the new Covenant).
MP isn't tarnished by reskinned leaders too. Every one of the 16 leaders have something unique in the table that the others don't. Additionally, each leader promotes different playstyles. Are you an aggressive rusher? Play Decimus. Prefer to sabotage the enemy? Go Shipmaster. Are you more of a defensive and/or economy type of player? Go Pavium. You'll eventually find your style.
Blitz is the P2W gamemode of HW2. Every card you get from these wretched things makes your units stronger to the point that a unit that has nothing more than a peashooter will be able to kill a unit which is designed to specifically counter that type of unit. Thankfully, it doesn't go beyond Blitz, but the gamemode itself could be a good beginning for players to learn how to micro-manage. Such a missed opportunity.
However, there's also a Firefight gamemode. You have to defend this important structure alone or with friends against increasingly difficult odds that will make you sweat. I did once and I'm very hard to sweat. You will need a mind of a commander to succeed.
If you're buying the game, consider buying the Complete Edition, giving you all the content released. In the Ultimate edition, you won't get the Awakening the Nightmare expansion and the said expansion won't give you the other leaders. The Complete edition is cheaper in the long run.