With the exception of Pokémon Go, relatively little is known about other Mobile Augmented Reality (MAR) games, and the attitudes of middle-aged and elderly adults towards them are hitherto poorly examined. The aim of this research is to examine the opinions of young, middle-aged, and elderly adults about the location-based MAR game Ingress. The responses to questions related to Ingress were collected from 24 adult players aged 20–60 from Greece and subsequently were analyzed by means of content analysis, both qualitatively and quantitatively, using the Jaccard index of similarity. Our findings showed that opinions of young people (20–35) agree more with those of elderly adults (>52) than with those of the intermediate age group of 36–51. It was also revealed that knowledge of geography facilitates the ability to play the game better, the game’s scenario is very interesting to adults, and the feeling of playing locally in a global game is also appreciated by all age groups. Along with these findings, with this research, it was shown that (a) content analysis is a valuable method for exploring opinions and attitudes of adult users towards MAR games and (b) Jaccard indices can be used to quantitatively explore themes emerging from content analysis.