Some believe a “gamer” is anyone who enjoys playing games, even including “casual games”. However, to subscribe to this definition is tantamount to saying that anyone who watches movies is a “film buff” and anyone who eats food is a “foodie”. That would be ridiculous because then literally 99% of those living in non-impoverished situations would be considered a film buff, foodie, and gamer; the terms would all become practically meaningless.
Most agree that true gamers enjoy something more than cheap games. For example, few people who play Angry Birds or Tetris for five hours a day would call themselves a “gamer” with a straight face (just like no one who eats nothing but McDonald’s every day would call themselves a foodie). On the other hand, “gamers” are usually associated with enjoying more artistic (Limbo, Journey), thoughtful (Braid, Portal), and/or big-budget (Mass Effect, Bioshock Infinite, Skyrim) video games.
These critically acclaimed games generally (not always) have either a very compelling and involved storyline, and/or immersive graphics, sound design, and musical score. I’m a fan of Garry Schyman and he was one of my instructors so here’s an example of a good musical score:
Comparing such a game to a casual iPad or browser game is similar to comparing a full-feature dramatic movie to a 30-second commercial. That is why many prefer the more strict definition of “gamer”. In the same way that people like to differentiate between “person who watches movies” and “film buffs”, and between “people who eat” and “foodies”, we like to differentiate between “people who play games” and “gamers”.
Contrary to popular belief, the purpose of this distinction is not to gloat from some ivory tower of elitism and say “you are not a true gamer”, but rather to reduce the probability of someone thinking that casual games or mindless shooters are all there is to “gaming”, in an effort to encourage people to discover a world of amazing games that most don’t even know exist.