Xenogears is not a series. XenoSaga is and Blade but they are not part of one another at all. Different IP's by different owners. Even if they were, I like Xenogears but it's hardly the best when half the game doesn't even exist. 

Dragon age

Origins is a masterpiece
2 is meh
3 is good (skipping fetch quests)
Veilguard is a disaster

Games where the first is the best:

The Legend of Zelda
Metroid
The Secret of Monkey Island
Double Dragon (Arcade)
Sonic the Hedgehog
Suikoden
Final Fantasy Tactics
Kingdom Hearts
Katamari Damacy
Dark Souls
Valkyria Chronicles

I've always said this about Bioshock and Metroid Prime.

Lots of good picks in here though - Splatterhouse is another one.

The first Metroid as in the NES game? 

Think I need to hear a reasoning for that one. Even if one prefer the old school 2D Metroid I find it hard to see what the first game does better than the GBA games or Super Metroid. 

I'm gonna cheat a bit and classify Metal Gear Solid as a different series from Metal Gear.

To me the first Metal Gear Solid is still the best one. The gameplay is very engaging and let's you have some fun with the stealth elements. The characters are memorable and the plot is full of twists and surprises without going off the rails like some of its sequels.

Gears of War (best multiplayer)
Animal Crossing
Bioshock
Donkey Kong Country
Paper Mario (I liked the first better than TTYD)
Ratchet & Clank
Pocky & Rocky
Wario Ware
Yoshi's Island
Mario & Luigi: Superstar Saga P
Pikmin

Which Metroid game did you play first Metroid or Super Metroid? (or maybe another Metroid)

I gotta say that I'm not a big Metroid fan. Tried a few of them but haven't finished any of them. Played most Prime and one of the GBA games. 

NES Metroid was the first one I tried. Felt it confusing and everything looked the same. Tried Super Metroid next and could not get used to the controls. Then Prime a lot later, liked it okey but have some sort of aversion towards the first person perspective. Played one of the GBA games for like 10 hours and found it really good, might return and finish it. 

I just cannot see anything the first Metroid does better than the rest of the series. So just asked what makes it the best in your opinion. 

That's a lot of hot takes for one post. Out of what id played i do not agree with any of those.