I LOVE CS:Source, so GO is a natural progression, especially for just $15. Wow. It takes everything that's good about Source, and ups the game with far better graphics, better guns, and new gameplay. "Arms Race" in particular is a friggin' blast.
I'm playing on my rMBP15, and it's smooth as silk at 1080p. The others are playing it on MPB13's, and it's still quite good on 720p.
I tinkered with it when it first came out, and I like it. I've always liked anything CS though from when I started playing it back around Beta 5.