One of the best things about the original starcraft, Nagromme, was that it was so much MORE than just an RTS.
most RTS games are just that... real-time strategy games, and while you might be able to find plenty of different maps, you're still playing an RTS.
Because blizzard shipped the original starcraft with a map editor (and community members then expanded upon that) people were able to make all sorts of maps that DIDN'T require super RTS skills.
While I loved playing the campaign, my favorite part of starcraft were the user-made multiplayer maps.
UMS stands for "use map settings." When you use map settings on a map, then the game uses whatever parameters and AI triggers were set by the map creator, and that means you can make all sorts of games from RPGs to my favorite - defense games.
Defense games can be played competitively or in teams. If I was playing turret defense, then I'd start with one builder unit and it would be my responsibility to prevent the enemies who start at the top of the screen from reaching the bottom. I'd have control of a thin "lane" and I'd be able to build missile turrets on it. The more enemies I kill the more money I get, and the more turrets I can build. Then if I get enough money, on most maps you can purchase upgrades or super-units, such as an air vehicle with good anti-air capabilities to help you out.
I recommend that you find the original starcraft and give it a shot, even if you only play multiplayer.