Oh well then I guess I get a chance to primp Xenosaga. Xenosaga is made by the same guy that did Xenogears and Xenoblade, so that's like 5 Xenos total.
Each one is slightly different. Xenosaga I is probably the best overall in terms of balance between gameplay, crazy storylines, music, etc. It was a lot of fun so props for that one.
Xenosaga II is very, very weird gameplay wise, has a worse OST, and yet despite all that I still managed to finish it and enjoy it for what it was, it's just not as easy to get into as Xenosaga I and III. One random battle took literally 110 minutes or something (ok maybe not), although that was mainly because I had skipped a lot of fights getting to that point.
Xenosaga III has the fastest and most balanced game, it is very complete feeling, and it also has a solid storyline that manages to conclude everything that was going on in a reasonable fashion considering it was originally planned to be 6 games.
Honestly all 3 are worth playing, IMO. Xenosaga I > III > II I think. TBH, Sometimes I think the Sagas > Blade... the earlier Xenos were very aggressive at exploring strange concepts and characters.
They all revolve around a lot of the same characters but Kos Mos is one of the main ones...

I guess the biggest barrier is that they are PS2 era but that doesn't really bother me that much personally as I still sometimes even desire to play PS1 era games. Also, I heard mixed things about the Last Story, I doubt it isn't at least somewhat fun though, and I personally have not played it.