The evolution of Tetsuya Takahashi's main Xeno projects from the mid-90s to 2017.

Final Fantasy 6

The first project worked on by Tetsuya Takahashi and Soraya Saga was Final Fantasy 6 - he did the Mech opening scene, she did Edgar and Sabin (the characters are represented in Xenogears, spiritually, as Bart's ancestors Rene and Roni Fatima)

https://www.youtube.com/watch?v=OU1W7b4B2tY
https://www.youtube.com/watch?v=_bKwoKA880s

Xenogears

This is the first game headed by Tetsuya Takahashi and Soraya Saga. Unfortunately, in the planning stages, Square gave the bulk of their budget to Final Fantasy 7, most of the people Takahashi got on his team were junior staff members. Xenogears was also in development longer than Square's 2 year time limit. Technology was also a limiting factor. All challenges considered,  they still released a classic. Then Monolithsoft was born out of this team, and they went on to make new games for Namco and Nintendo.

https://www.youtube.com/watch?v=HSc59wy4aT4
https://www.youtube.com/watch?v=rjyh94S8Gkk

Xenogears Perfect Works - After the completion of the game, there were some remaining ideas and assumptions existing in the heads of the writers about the universe, that never made it into the story. This companion book that gives a little more background into the universe of Xenogears; it acts as a sort of an appendix to the game - similar to that found in fantasy books, such as Lord of the Rings. Hyrule Historia would be another example of a book along these lines. It never had an official release in North America, but all hardcore Xenogears fans (those around in the 90s at least) know its contents. A fan translation can be found here: https://www.flickr.com/photos/29956195@N08/sets/72157616593453778/

Xenosaga Episode 1

This was likely Takahashi's highest budgeted game until Xenoblade Chronicles X. It began a series of very ambitious games, originally 18 were planned, then 6, and then finally 3.

https://www.youtube.com/watch?v=b_pC4juVZ6M
https://www.youtube.com/watch?v=SfsnfJpW6cc
https://www.youtube.com/watch?v=Aj5iz8iDxh8

Xenosaga Episode 2

This would be Soraya Saga and longtime character art director Kunihiko Tanaka's exit from the team; neither having much influence on the final product. Most people who played this game, and the others, can recognize the lack of spirit infused into these games from the previous titles.

https://www.youtube.com/watch?v=75V6z6j6Bxs
https://www.youtube.com/watch?v=GV7_sTV1lpk

Xenosaga Episode 3

With a low budget, and an uninterested Tetsuya Takahashi, the remaining team took notes from the original creators managed to put together a game that is arguably the best of the trilogy. While the lower budget obviously shows, the return to a more Tanaka-style art, and putting in many of the scenes Takahashi and Saga wanted in the game really helped it out. In the end, the game did feel a bit like Xenogears disc 2 the whole way through.

https://www.youtube.com/watch?v=NYPTJMujz1E
https://www.youtube.com/watch?v=Yhl8CiWal2I

Xenoblade

The first game Takahashi did with Nintendo. The main focus was an experimentation in large scale landscapes, which didn't work out as well as he hoped in Xenosaga, as well as a vertical travel design. While differing in detail, the plot uses re-skinned plot points from both Xenogears and Xenosaga, although in a very reduced form. Takahashi had failed to see his full vision realized multiple times, and instead saw this as an exercise in toning it back while focusing on other elements. It was, of course, very successful. 

https://www.youtube.com/watch?v=8_syBQwHe9k
https://www.youtube.com/watch?v=PPzanONuO9w

Xenoblade X

The first truly open world game Nintendo ever developed. Takahashi took the learnings from Xenoblade and made a game which much more resembled Xenogears and Xenosaga in detail, although still not with a very extensive plot. Instead, the plot used a very open world model where players could meander their way through to the end - although, not truly as open world as Zelda: Breath of the Wild - as it still used the model of multiple opened chapters, but a critical path that the player had to follow down in order to open up each new set of quests. These critical path events surrounded developments in New LA and the world arround; this was so the world could evolve, and give the player much to do, and whole new ways of tackling it.

https://www.youtube.com/watch?v=luTV6fUubdI
https://www.youtube.com/watch?v=2uYFpfB3DWc
https://www.youtube.com/watch?v=hXebYygyEJo

Xenoblade 2

We know little about this game at this point, Takahashi has never been so quiet on a project prior to release. What we do know is that it takes open world elements, but instead has a main plot built in. I am not really sure what he means by this, but I am optimistic, because even in his "failures" brilliance tends to be the result.

https://www.youtube.com/watch?v=Xjpao-nD5YU

Xenogears will always be my favorite work of theirs. It touches subjects and story archs that games today wouldn't dare touch. And it was executed in such a perfect manner. Match it with Yasunori Mitsuda's amazing score and you've got a masterpiece on your hands.

Can't wait to see what they've done with Chronicles 2.

"I love this world because you're in it"

That's the kind of dialogue that points the peak of a professional career of 23 years.

Lmao! thanks for making me laugh xD

I realized I forgot to mention the other person who was booted during this period, character designer Kunihiko Tanaka. He worked on Xenoblade Chronicles - I am not sure what his role was in that game, but in Xenoblade Chronicles X he returned as character designer - and in my opinion it brought both progress and nostalgia back to that game. 

Anyway, on the topic of Soraya Saga and Namco. I am not sure the full story that occurred, but it was during this game that Takahashi became very upset. Obviously Soraya Saga was more upset. I think out of professional courtousy, they held back what was really on their minds: that Namco were humongous assholes who wanted to exploit their reputation, and had no interest in the artist's vision. Of course, it could be that talks broke down and both sides had gone a little overboard - I recall that Namco had reported Soraya Saga being difficult. Either way, I don't think we got the best outcome for that franchise. At least the Xenoblades seem to be going very well. The team is also more mature and much more experienced now.

On a side note, Takahashi was supposedly the loudest and most charasmatic person working for Square by various reports.

Same here, still my favourite game of all time.

Speaking of Mitsuda, I forgot to mention much about him in the process, as he's been a major figure with Monolithsoft. First working with Takahashi on Chrono Trigger. On Xenogears, Mitsuda actually didn't have the time to complete all the planned music; he had a lot of conflict with Square - and stuck around until Chrono Cross, mostly because he was seen as the star developer on Chrono Trigger. Apparently he became so stressed working on Chrono Cross that he was hospitalized after degrading health and a panic attack. While he hasn't been very open about his struggle with Square, I think his action of never working with them again speaks strongly.

Chrono Trigger is missing. Tak worked on Chrono Trigger.

All I can say is I love their work.
Those games are all fantastic.

They consistently deliver quality in the story department, even if in the gameplay department saga 1 and 2 weren't so strong.

Yeah, 18 just sounds insane, now sure how long that was planned for, because there's no feasible way to have done that.