The spiritual successor of Starcraft is Stormgate. I cannot comment on it, I have no idea how good it is. AFAIK it is multiplayer only. I played Dune II, Warcraft II, C&C, Red Alert, Starcraft (didn't like, I never understood the hype), Dark Reign, Total Annihilation, Warcraft III as kid, but... only single player (at various difficulties). That is just how games were generally played in the 90s. I do remember using a null modem cable at some point, but IIRC was only to play Doom and Duke3d.
I believe the RTS genre at a whole got superseded by the MOBA genre (with DotA and LoL). A genre I tried once (HotS) and was terrible at. If you're shit and you're not improving (I didn't enjoy it either, I felt forced to do it for a reward in another game), stop trying. I never tried any other MOBA, except maybe a touchscreen one, Warcraft Rumble? Either way, I got burned by Hearthstone Mercs and fell once more in the trap with Rumble. After Blizzard announced removed of addons from combat, I've finally said goodbye to the Warcraft franchise and Blizzard in general.
There's one game I really do like which has a kind of RTS with map feeling to it: Total War: Warhammer series (though I laud their BS with DLCs and multiple game versions). I suppose the whole Total War series is as good, I just like the Warhammer universe. The other day, Settlers II was discussed on here, including a FOSS clone. Settlers II is also a game I liked (III not so much though artwork was nice, never played the orig.). Supposedly it isn't RTS, tho I am pretty sure back then it was called RTS.