I guess the only other real series I played was
.hack//G.U. from
Bandai-Namco.
A three volume series that could've been confined to one release, but it was just a marketing ploy to make money, and since I bought all three games, it works
I did enjoy playing it, so I can't really complain.
I'm also working on and off on
XenoSaga, also a 3 game series.
And I guess I should include
Devil May Cry as well since I played the first three games. Probably the goriest game I can play without feeling squeamish, and I know there's some messier stuff out there
Other non Square-Enix games I have but own only one of the series:
Shining Force Neo
Persona 3:FES
Suikoden IV and Tactics
But, the majority of my games ARE Square-Enix, and
Final Fantasy series is the largest series I own (FFI to FFXII except III and XI, and including Tactics, FFX-2 and DoC), and then the
Kingdom Hearts series is next with only 3 games.