More than half of my gamecube library is third parties, of course, i almost ran out of first party games to buy. I'd say that over half of my GBA games are also third party, probably 1/3 of my DS games. Half of my SNES games.
However, 95% of my PC games are third party (microsoft does publish games) and about 90% of my PS2 games are third party. Combined those completely destroy my total Cube games.
As i had to try to explain in a different thread on a different forum, there are wonderful game titles everywhere - all you need to do is broaden your horizons and try to find them. My taste in gaming appears to be more diverse than most, I rarely find "lemons" (though i do come across a few - PoP: Warrior Within) but overall my focus has actually shifted away from Nintendo and more towards PC games.
This is coming from someone who lives Nintendo so much that he actually got a nintendo icon tattooed onto his body.
Give things a try.
Actually, cause i'm bored and need to fall asleep - i'll give exact ratios!
Cube: 20/60 are first parties. (I was even a bit lenient with calling things like F-Zero GX, Cubivore and Battalion Wars first party(Cubivore, oddly enough, was created by Nintendo but published by Atlus *shrugs*)
GBA: 16/36 are first party.
DS: 8/13 are first party (I need more DS games...)
SNES:17/40 are first party (being lenient again - counted my 4 rare titles as first party)
So, only the DS has a majority of nintendo first party titles for me, even for my Nintendo systems. (I didn't bother counting my other hardware, PC, PS2, PS1, etc.) I can't claim that my favorite games on each systems weren't first party - but i'm sure that my top 10 per system is probably a half-half First party/third party ratio.
My amount of PS2 titles is quickly approaching my Cube title collection - i'm sure it'll beat it out before i'm done. (Partly because a lot of my PS2 games were free - but let's not get into that)
Also, i don't hate the N64 - far from it. I just no longer own one, or any of the games associated with it. This is a combination of thievery and a hurricane. However, i owned 25 games and i'm sure that the ratio was about 50/50 with that system as well. (I think it was actually a bit heavier on third parties if i remember correctly)