Halo 2? On Legendary? Beaten by a below-average player? Either there's BS here, or it took a retardedly long time. The original got pretty easy once you got the hang of it - the second did not. And anyway what's so wonderful about it being really difficult? That's not an inherently good thing, in fact that usually works against something. Also, Mythic difficulty.
Half-life was so uninteresting that I used god mode after getting halfway through, just to see the end of it. After so much hype about it I figured I must have been missing something, or that staying the course would reward me - it didn't. So yeah, I consider it overrated, because everyone talks about what a great plot it has, when I barely even see a plot:
Scientists mess around with something they shouldn't. Disaster ensues. Only one person is capable of cleaning it up. He is attacked not only by whatever consequences there are of the mess itself, but also whoever the incompetent and immoral government has sent in to clean up. Never seen that before. It's not original, but that would be okay if it were well told. Which it isn't.