My main beef with the Gamecube was that coming off the N64, so many games felt like a huge step down.
On the 64, we got Ocarina of Time, a timeless epic that was like the Lord of the Rings of video games. On GCN we got Wind Waker, which looked like someone threw up paint over an episode of the Powerpuff girls, had crappy dungeons, was shamelessly padded out with filler, and revolved around the agonizing slow and boring sailing.
On 64, we got Starfox 64, an epic space opera that felt like the Empire Strikes Back of video games. On the GCN, we got Adventures, a third-rate Zelda clone with boring level design, ear-bleeding voice acting, and the most annoying sidekick of all time.
On the 64 we got Mario 64, an extravaganza of memorable worlds, tons of variety, and cool challenges. On the GCN, we got Mario moonlighting as a janitor on a monotonous resort setting.
It all just felt so watered down.
That's exactly how I felt about the software. The first party software felt like Nintendo had lost a step coming off the N64 which, despite having the monumental blunder of going with cartridges, still managed to come off with some very magical software.
Sunshine, I can't ever get behind this game. It didn't feel like a Mario game at all, let alone a 3D Mario game. It completely lacked the diversity that made the others feel like some grand adventure (even the first Super Mario Bros). The variety characterized every other mainline Mario game in existence (is Sunshine even a mainline Mario game?), including most of the not-so-mainline ones (like 3D Land and World). There was something very flat about the game. I got the same feeling from 3D World, but at the same time, it had the diversity - so it felt like a nice throwback.
But for someone a little taller than most, larger hands, the controller always cramped right above my thumb most games. Plus the button configuration made certain fighting games impossible. Try playing Virtual Console games from SNES on Wii with the Gamecube controller, because many of them have three-button transitioning, they don't work very well. Super Mario World was virtually unplayable, but it was still a fine compared to the nightmare that was Street Fighter 2 on the Gamecube controller. It's not just the weird trigger buttons, or the bizarre face buttons that made action games more difficult, but also the fact that the d-pad was more or a less a functional decoration.
Animal Crossing, I'll give that one to Gamecube fans, that one was a lot of fun, and one of the few games that didn't cramp up my hand after 10 minutes, and it was a unique experience that was a lot of fun.
But Pikmin? That's one of those games that seems like I should have loved (I loved SimAnt), but found terribly uninteresting; I think the series has potential, but the GameCube game missed those brass rings. Eternal Darkness? Was as unremarkable as Survival and Horror games get - the historical setting was a nice idea but poorly executed as the game failed to capture the essence of any of its time periods, the action was sloppy, and the insanity system was gimmicky at best (there's an indie game called Don't Starve, that's how to do an insanity system), but its real failing was that it was one of the worst balanced games I've played, ever... it made TMNT on NES feel reasonable.
All in all, the Gamecube was kind of like the darker half of the dark age for Nintendo. But the console was a bit of a stopgap.