Depending on what you like about StarCraft…
The Warhammer 40k RTS games are great. Red alert is also in the same vein. I thoroughly enjoyed Halo Wars for a few hours.
If it’s the base building and creating a death ball, Age of Empires games.
If it’s just the base building, Against the Storm.
Halo Wars honestly just works imo. Both games. Like honestly on paper, everything about it sounds like it’d be a hit. And it kinda was; I feel like a lot of people ignored it because it wasn’t a mainline Halo game. I know I did for a few years until I got a chance to play it, and loved it.