It's interesting seeing people say things like "accessibility" or "easy to start, hard to master". As an older fan who grew up with the "great" games, terms that I would use would be big, challenging, groundbreaking, technologically advanced and well-executed. I can remember when SMB came out it was a technical marvel and absolutely massive compared to anything that came before it. Like 100X the size of Mario Bros. People would talk about secrets in the various worlds, and they seemed endless.And then SMB3 came and put it to shame. Zelda 1? Well that was on another level of complexity and epicness of any title.
I also remember the great level of polish on those titles. Picking up Castlevania after playing Mario was like walking in quicksand. The controls were brutal in comparison, and the levels far more unfair and flawed. Few games could match the execution of concept, Mega Man, Contra and Final Fantasy being notable exceptions.
Moving forward to later great games, DKC had CGI graphics beyond anything on the market, and F-Zero was nothing short of revolutionary. Mario64 and Zelda OoT basically destroyed anything on the market for complexity and production values.
So what made them great? Everything about them. If judging by modern AAA standards, they would be AAAA games. Graphics, sound, challenge, control, size and value. The most ambitious games in the industry, and it showed.
