Objection 1: "The best part of the game is the social". People have great stories of the folk they've met through the game, the events their side has organized, and so on. All of this is true, and none of it is relevant. Ingress is a social game in just about the way that golf is a social game. There are things you can do in Ingress if you have more than one person around, but nothing in the Ingress game rules or structures requires cooperation or teamwork.
If you like, compare Ingress with chess. To play chess the rules require two people playing opposite each other. We've added rules that let people do things like play chess by mail so no actual social interaction is needed, but those are rules outside the basics of chess. Chess is a social game; Ingress is not.
The social that comes with Ingress comes as a result of the people involved. People form social interactions around bird watching, bowling, and barbecue. All of those social things are great, but none are required by the underlying activity/game. Compare with basketball or baseball, which are inherently team games. You can do lots of things with baseballs and basketballs by yourself, but that's not playing the game. Likewise with Ingress, you can do lots of things in groups, but the game itself doesn't require it, isn't structured to reward it, and can be a completely solo activity without missing out on anything. Ingress fails at social - some people who play Ingress win at social, but I suspect they'd also win at social if they were organizing dinners or backpacking expeditions or anything else. No credit goes to the game for this.
Objection 2: "It's a great way to get exercise." This one has more merit and at times I've called Ingress the ultimate gamification of exercise. The rules of Ingress portals are such that in theory you should be able to walk to them, though portals have been set up on the tops of mountains and in other locations that are hard to reach by standard walking. But I don't think Ingress does anything particularly novel here - every AR game is situated in the world and requires you to go out and be in the world.
The notion "well, I walk more now that I'm playing Ingress" is also a particularly situated notion. It's great if you're in an area that accommodates walking well and the weather is good, but when you're dodging cars in the dark because the sun went down at 16:30 and the outside temperature is 22F before the wind chill, this whole "I walk to play the game" conceit melts away quickly. Not that I've, y'know, ever done that.
Yes, I get more exercise playing Ingress than if I played a desk-bound game. But I also get more exercise because I have a dog and she needs to go for walks, too. It's not a particularly great point in favor of Ingress-as-a-game.