Wings of Liberty : 1st campaign, with terran. Good experience, I liked the story aswell.

Heart of the Swarm : 2nd campaign, with zerg. Better than WoL (but also maybe because I'm a fan of zergs and Kerrigan). Very good experience overall.

Legacy of the Void : 3rd and last campaign, with protoss. Was less good than HotS, also because the missions were a bit repetitive, but still a good experience, BUT... The last 3 missions are EPIC AS FUCK, I even had tears of joy after finishing the latest one. The end of the story is $$$$$$$$, Kerrigan is such an interesting character, it's amazing. FUCKING EPIC ENDING. PERIOD.

If I had the rate the singleplayer of this game I would give it a 18/20.
Do I recommend it ? Yes, ofc, at least for the story and characters design and personality. But if you don't like RTS games, then just watch the cinematics compilations on youtube, they are worth it :).

Also, with my new pc setup (i5-6500, GTX 970, 8GB of RAM, SSD, 144hz 24" 1080p monitor), I played with maxed out GFX, and despite the fact that the engine is like 6+ years old, it still look amazingly good (except some textures look shit when you're too close to it). And I didn't experience any lag, I'm not sure if I was at 150+fps even in huge maps with huge ammount of units and buildings, but it was still very smooth in any situations.