I enjoy Age of Empires 2 now and then.
I'm pretty bad at it, but I still find it fun to play against other people.
I don't enjoy it against the AI so much though.
I though Halo Wars 1 was kind of fun, the campaign and skirmish against the AI some.
Favorite RTS I've played is probably,
The Lord of the Rings: The Battle for Middle-earth II,
'Really liked the War of the Ring in it, which was kind of like a Risk Map, where each fight was a skirmish,
Making heroes was fun, and I found it fun to delete them if they died even once.
Campaign was fun.
Not 'easy to get the game to work nowadays though.
Command and Conquer Generals was pretty awesome,
Bit over the top in a fun amusing way at times,
Awesome campaign.
Warcraft III (Not Reforged)
Has a good campaign, though I would have liked some 'choice in the ends.
Warcraft 2, I still like, but 'do think it feels dated.
StarCraft 1, has a great Sci Fi campaign and story,
I've never tried StarCraft 2, don't plan to.
Warlords Battlecry 1,2,3
I enjoyed all, though they are a bit dated,
Campaign was challenging for me in 1,
2 had a cool Risk style conquer the world map,
3 was alright, 'hint of rpg to it.
. . .
For me, playing against the AI in some games can be lacking, Age of Empires 2 as an example.
Part of this is due to the limited actions of the AI, the lack of 'imagination so to speak.
But I think there is also a lack of 'competitiveness.
It's 'fun to fight another 'person.
Though story/campaigns against the AI can be fun, due to the variety of the scenario, as well as 'advancement.
Perhaps it would be good if some skirmish games against AI had ELO you had to maintain,
If it had unique AI of different skills and personalities,
Such as an AI that if it was your ally in a game, and you stole their resources or called them a noob, the AI then tries to wall you in or attacks your structures with mangonels.
A real cheap fighting game I played once, Final Slam 2, had a fight system where you competed against randomly created AI fighters, could become champion, and keep getting challenged by fighters. Could be difficult if you grabbed every championship and were challenged every day, unable to rest and recover health.
Had personalities you could set for the AI, that caused them to build certain units more, expand more, burn cities when they took them over more or the cities were threatened by your armies.