What made banjo-kazooie and banjo-tooie stand out for me was the way the secrets kept lingering on in my mind for months, without the internet providing any answers whatsoever to the mysteries.
...probably because most of the secrets were never fully implemented (stop 'n swop) but yet... They continued to make me look for more, adding great atmosphere and replay value to seek every nook and cranny, every possible button combination in every place remotely off.
Rareware at that time kept the secret going at their "scribes" (former website Q&A) By providing vague answers to these secrets when inquired.
I loved it, only thing I didn't love was finding out they dropped the whole thing :/ it was never finished.
GTA V manages to do the same thing with the secret of mount Chilliad, since noone has found the jetpack yet.
Please playtonic, make the best hidden mystery of all time in this game, that keeps me exploring and investigating. A mystery so vast, it will make the whole game developers community regret their poorly hidden easter eggs.
I miss the days looking for a way to make the rusty bucket set sail once again, finding the lava world, opening the 2 big doors in gruntilda's lair, finding devil bottles and solve stop 'n swop... Not to forget DK64: finding out what the pillar was good for.
Make it work and continue to inspire further exploration and take my money.
Stop picking your nose