That is one of the few reasons I still like this place, despite all the evidence you guys remain optimistic and positive but not fanboyish like other sites and not constantly negative like pretty much every other site out there. This place has a good balance of common sense and love for Nintendo. I for one will always love Nintendo but I do think they have made some mistakes over the years that are making it harder and harder to support them.
To answer the question of the thread, the only Nintendo purchase I have ever made I was disappointed with was Zelda Wind Waker and Luigi's Mansion, I really wanted to like those games but I just couldn't as hard as I tried. I knew what I was getting into with Pikmin and at that point I was just happy to have something fresh to play but even that wore off but it wasn't a disappointment it was just too much going on in one game for me to stay focused, plus at the time I was really deep into Harvest Moon AWL and that game took all my attention. Also I really hated DK 64 despite loving DKC.