I think it's cool because it's basically a replacement for a console. You buy the game you want to play and it runs on Google servers and streams the game video directly to you, so there's never any downloads or updates or anything, and you can run even the most demanding games on basically anything.
You basically just download an app to play on your computer, laptop, phone, tablet, or TV, and that's it. Unless you're playing on a TV (where you need a Chromecast and the official controller), you can use any keyboard or controller you already have and play console-quality games wherever.
I'm trying to decide whether to get Borderlands 3, RDR2, or Final Fantasy 15 next. You still have to pay full price for the games (most of the time), but not having to buy a console and also being able to play on my laptop, then pick up and play a bit on my phone, then play at night on my TV is pretty rad. The only downside is they don't have a ton of games supported yet, but it feels like they add a few each week.