While it would be untrue to credit Starcraft 2 for the explosive rise of eSports in recent years, it was timed almost perfectly. And if it's intended to be a competitive experience, as with Starcraft 2, then it will be fine-tuned and expanded whenever necessary.
If it is growing stale then it will get regular new content, as with WoW. If it has problems, real problems, then they will be fixed - as the company tried to do with Diablo 3. A Blizzard game does not have a fixed lifespan. Starcraft 2 showcases what Blizzard is better at than almost every other developer, with perhaps the only comparisons being Valve and more recently Riot. After a while I moved onto other things, then 2013's Heart of the Swarm pulled me right back in - new units being the most obvious draw, but the shaking up of a tired metagame being the real secret sauce. I watched it all the time, followed the tournaments and the Korean GSL, and studied the strategies of players I especially admired.
I got decent at it too, hovering around Platinum League with occasional forays into Diamond - the Koreans were hardly quaking in their boots, but I could hold my own at a reasonable level.
For around two years of my gaming life I was obsessed with Starcraft 2: Wings of Liberty.