I define a hardcore gamer as anyone who almost constantly plays games, regardless of what type of game. If someone decides to focus on one game, then they would be a hardcore <insert game name here> gamer, whereas someone who plays a wide variety of games nonstop would just be a hardcore gamer.
As for what the games today are like compared to that of the past, I'd say that anymore the majority of game companies focus on trying to get as much money as possible. They do this by making shiny things to catch people's attention and make it pretty because apparently that's what the people who like shiny things want. Back in the days of the SNES (what I started playing), they couldn't make things all that pretty, so they focused on gameplay. There are a few companies today that make games that focus on gameplay, but they seem to be the minority.