I agree that I am feeling the same way about the Zelda series right now.
I am also glad to see that you've singled out Nintendo for their franchise milking. After all, it's [http://en.wikipedia.org/wiki/Final_Fantasy#Main_series] not [http://en.wikipedia.org/wiki/Tomb_Raider_series] like [http://en.wikipedia.org/wiki/Half-Life_%28series%29] any [http://en.wikipedia.org/wiki/Metal_Gear_%28series%29] other [http://en.wikipedia.org/wiki/Gran_Turismo_%28series%29] company [http://en.wikipedia.org/wiki/Duke_Nukem_%28computer_game%29#Sequels] have [http://en.wikipedia.org/wiki/Tony_Hawk%27s_%28series%29] made [http://en.wikipedia.org/wiki/Resident_evil_series#Games] game [http://en.wikipedia.org/wiki/Call_of_Duty_%28series%29] series' [http://en.wikipedia.org/wiki/Sonic_the_Hedgehog_%28series%29] that [http://en.wikipedia.org/wiki/Crash_Bandicoot] have [http://en.wikipedia.org/wiki/Hitman_series] grown [http://en.wikipedia.org/wiki/Grand_Theft_Auto_Series] repetitive; [http://en.wikipedia.org/wiki/Ratchet_%26_Clank_%28series%29] now [http://en.wikipedia.org/wiki/SimCity_%28series%29] I'm [http://en.wikipedia.org/wiki/Need_for_Speed#Need_for_Speed_installments] just [http://en.wikipedia.org/wiki/Burnout_%28series%29] extending [http://en.wikipedia.org/wiki/The_Sims#Sequels] this [http://en.wikipedia.org/wiki/Silent_Hill_%28video_game%29#External_links] sentence [http://en.wikipedia.org/wiki/Tom_Clancy%27s_Rainbow_Six] because [http://en.wikipedia.org/wiki/Tom_Clancy%27s_Ghost_Recon] there [http://en.wikipedia.org/wiki/Splinter_Cell#Games] are [http://en.wikipedia.org/wiki/Battlefield_series] so [http://en.wikipedia.org/wiki/Quake_%28series%29] *many* [http://en.wikipedia.org/wiki/Warcraft#Computer_games] examples [http://en.wikipedia.org/wiki/Soulcalibur#External_links] off [http://en.wikipedia.org/wiki/Dead_or_Alive_%28series%29#Main_series] the [http://en.wikipedia.org/wiki/Midnight_Club#Games] top [http://en.wikipedia.org/wiki/Halo_series] of [http://en.wikipedia.org/wiki/List_of_Star_Wars_video_games#Series_titles] my [http://en.wikipedia.org/wiki/James_Bond_games#List_of_video_games] head [http://en.wikipedia.org/wiki/The_Elder_Scrolls] (I even had a few more, like Doom). As Yahtzee would say, 'Quod erat demonstrandum'.
The entire videogame industry is become stagnant and stale - my point is, this is not confined to Nintendo, and whilst they certainly have been 'doing it' longer, and definitely are one of the main culprits behind franchise recycling, plenty of other companies also do this - Yahtzee acknowledges this in his first video which mentioned how similar Resident Evil 5 looked in gameplay terms and synopsis to Resident Evil 4, Yahtzee also notes in his review of the Orange Box how the set pieces in Half Life 2 are becoming familiar (Similar scenarios, that damned see-saw based puzzle). Granted, Zelda takes it further than that and I'll admit the premise of Zelda games follow a formula.
All this said, I'm starting to find many games (particularily FPSes in general) are beginning to feel very generic and all like each other. I think most developers, not just Nintendo, need to try something original. And this is gonna sound like the cliche' of all cliche's, but the Wii is probably the most 'original' console, given the other two are more powerful versions of their predcessors (with more pretty versions of previous iterations of games) - it's just the fact there's hardly any compelling software which is the problem...
That aside, Yahtzee did make some good points about Zelda, Phantom Hourglass. And, like practically everyone else has said, nice Okami reference near the end.