What's the core obstacle of any game for a player to overcome (whether it be chess, videogames, or basketball?
Punishing/Penalizing you when you lose/fail. And from that failure, you learn how to better deal with whatever challenges the game (or your opponent, as in the case of sports or compe ive gaming) is presenting. When you get infinite lives and continues and always start from a convenient checkpoint, I think that undermines the idea of what a game is supposed to be. It's why modern games are more like interactive movies to me than actual games. Doesn't mean they're not fun, but good game design (to me) creates a compelling challenge that questions your certainty (i.e. Can I beat this game? Figure it out?). When I played Rise of the Tomb Raider, I already knew I was going to beat it before I ever logged into Steam.
Minecraft isn't really a game, more of a virtual Lego set. That's not to say it's not cool for what it is, but I can't really classify it as a "game." Portal is great. Like I said, there's always exceptions. Portal also comes from the cusp of when gaming started to get really dumbed down ('07), so Portal still retains that classic spirit imo.