I could never get in to the Galaxies, I used to love those kind of games when I was younger, but the older I got, the less interested I was in them, it's not an age thing though, it's just I went in a different direction gaming wise.
Why do you feel they were downgrades? Was it the controls, content or something else?
Never been a fan of the Mario Kart series either, I thought Brawl was alright though.
Never played any of the others but Metroid is one of the biggest series I've never played but was interested in.
Well, like I said it's mostly a subjective thing. The GC was always the party console for my friends & I, and as such we spent hours and hours playing a mix of Mario Kart DD, Smash Melee, Mario Tennis & Strikers. I know my views on the later games are probably strongly influenced by this, but I can't help it xD
I can't really speak for Wii Mario Strikers, as I never owned it - I played ~10 hours the week after release at a friends house, and we just kept gravitating back to GC Mario Strikers. Can't really remember why, but I believe our biggest problem was they slowed the game down quite a lot.
Smash Brawl is a good game, but for Melee players the 'problems' are well documented xD Tripping, the floatiness, the smash balls... just so many things they changed from Melee, arguably for the worst. There's a reason the competitive scene is still (mostly) playing Melee after all these years.
Mario Kart also has a number of problems: Battle Mode is drastically changed (gimped, to me), I was never a big fan of the controls (it always seemed looser than Double Dash), and I felt the Track Design was also a step below. Of course, Double Dash was probably the game I played the most in High School/Early College, so this might just be me preferring one play style to another.
This isn't saying any of those games are
bad, per se, just not as good as their predecessors. Of course, some of my complaints are surely subjective things that others won't have a problem with, but for me (and my friends at large) a working GC is still a must for any Game Night.
I think my problem with most of these games (though I'm sure most people will disagree on Mario Kart at least) is that it seems Nintendo tried to make them all a bit more accesible. This is fine, and seeing as they're all party games it makes sense. But when you spend so many hours playing them semi-competively, some of these changes just aren't made for you. I also don't really agree (especially with Smash Bros.) on
how they went around doing this - its fine to lower the Skill floor, but this shouldn't mean lowering the skill ceiling as well.
As for Metroid, it's really a great series. If you can somehow get Prime Trilogy, the wii controls are great for all 3 games and it's very much worth a buy (It's a steal too at retail price, $50 for three near-masterpieces)
TL;DR - I'm probably just too used to the GC games, and the (perceived) change of direction of their Wii counterparts didn't gel with me.