Personal ranking of how I view the series after playing a lot of them. Been thinking about Rankings for a while and realized I could make it a bit more interesting. So I'm still going to label it as rankings. But in addition to that for any other's who want an archive of sorts full of tips, guides, how to emulate and additional material I'll add here enclosed in each note.

Useful Infographic on Xeno Series

My Personal Suggested Play order:

Any Xenoblade game you can start with. With some exceptions
3 has better impact if you play 1 then 2 then 3. Not going to say anymore than that. Also I'm begging you to play Future Connected from XC1. Torna from XC2 and Future Redeemed from XC3. The former is an epilogue after 1. The latter are prequels for 2 and 3. Providing massive backstory, lore on the events prior to their respective games. Both these expansions/epilogue I feel should be played after beating the base game.
* - If you start with XC1 please play the definitive edition since it includes Future Connected. The 3D and Wii versions do NOT include it. Alternatively one could watch a let's play on it... :D

Xenosaga games you must start with the first. Or else you will be lost on the narrative from 2 and 3. Additionally they have extra material I feel not many people know in the form of drama cd's, phone games(pied piper) and perfect works. The former greatly enhances your experience while playing through the games much like how Trails has with Drama cd's + manga. The latter perfect works is best read after finishing the whole trilogy for any further information regarding concepts, characters, story and more. Think of it like the Xenogears Perfect Works guide.

Xenogears. The OG bigdaddy that started the series. Has many elements/references/easter eggs that trickle down into the saga and blade games. You don't need to start with the OG. But man it helps quite a bit in understanding the themes, messages, character types and so much more later on in the series. You can play this anytime. But personally, I'd start with it.

Xenoblade X is fine to play without any prior knowledge to the above. It is not a sequel to the prior games and is more of a spiritual successor.

Additional Material:
Xenogears Perfect Works translated - Think of this as Ultimania of Xenogears. Full of cut-content and what could've been. Best to read this after playing the base game.
Last Xenogears novel has finally been translated - Story takes place before the events of the game.
Xenogears Comic Anthology translated - Best to read this after finishing the game. Since it contains short stories from the past, present and future.
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Xenosaga Series tips
HD Remaster for Xenosaga trilogy
Ordo ab Chao: A Guide to Understanding Xenosaga - A Fan guide to understanding the Xenosaga franchise
Xenosaga Series Perfect Guide

A final note: I don't consider myself an expert on the series. But for any newcomers who want to give a try on the xeno-series from a casual xeno fan/lore dude. I hope this list/guide helps!

Part of my Rankings + Beginner's Guide Folder - A series of lists where I place my rankings on games I've finished in various genres/series, but also try to input a beginner's guide when I can to keep them interesting beyond a ranked list.