honestly, im not that big a mgs fan, but the upcoming nintendo exclusive looks amazing, and certainly falls under the "mature" heading you're looking for
other games like that would include the resident evil series, metroid prime, eternal darkness, star fox adventures, etc.
in all honesty, tho, i just don't really get the "grown up" argument. yer certainly not the only one to express it, tho -- thats the argument most all ps2 users use (and thats nearing 15 mil!).
i have a blast playing mario games, mario kart, super monkey ball... and i'm 24. i never knew there was an age requirement for fun or gameplay, so i never bothered looking at games that way.
hell, tetris is filled with colored blocks and pacman is a lil yellow guy chasing ghosts, but those are games anyone can pick up and play anytime, because they're fun. games that have lasted solely on their fun factor for decades.
would pacman be better if he shot the ghosts to a bloody demise? its possible. but probably not.
why apply an age to fun?
