At some level I've always had to respect Mario 64 for it being seemingly a great experience for most people, but I have never been interested in playing it to the end. I play the first few levels and only get the stars I need and once I hit Lethal Lava Land I lose interest... ┐(ﾟ～ﾟ)┌
Anon above mentioned Half-Life which I funnily enough have a similar experience with too, I liked playing Sven Co-Op and other mods for it but was never blown away by the game alone. Half-Life 2 was even worse to me... (;´Д`)