Xenosaga...hum, what a person with an username like mine can say about it? lol
Xenosaga I was a pain in the ass. With a bad pacing and story development, it's easy to give up on it. Also, the OST was badly used, to the point that no dungeon in the whole game (apart from the LAST one) has a background song. The battle theme is the same as well, apart from the last battle (thank God, the last battle song is amazing). The cutscenes were too long, and that made the game seem even more boring than it really was. The battle system...in the beginning it was nice, but latter in the game it becomes boring as well. It's too slow, and Xenosaga II takes this to a WHOLE NEW LEVEL. As for characters...Shion was already bad here (nothing like 3, though), MOMO was a Sakura copy/parody/whatever, Jr. ... god. KOS-MOS had some interesting moments, though. Well, she used to disobey Shion back then, that makes she gains some points with me.
Then...Xenosaga II...Can't even believe in what they did here. OST was a tragedy (I'm talking about the game one, not the one made by Kajiura), and many of the songs composed by Kajiura were badly used (no matter how good a OST really is, if the songs are not well used it will mean nothing). Characters...which characters? This game was almost solely for Jr. and Albedo (if it were just Albedo I wouldn't complain, though. Few antagonist manage to cause such an impact as he did), Shion was almost forgotten (Good point, actually LOL), among other things. Battle system was even slower and more boring than the one from the first game.
Xenosaga III...now here's where Monolith surprised me. After two failed attempts to follow in the footsteps of Xenogears, they somehow managed to create an entertaining game that was able to link all the previous games into one good conclusion. The battle system brought no innovation at all, but it was fast and entertaining, something they never managed to do (and I include Xenogears here as well). Music was splendid, since they actually used it in a good manner (there were what...more than 10 battle themes?), the plot flowed well (with a little drop in the second DVD, but they managed to recover from it). THE problem of it was...Shion Uzuki. Never will I meet such a dreadful, ridiculous character such as her. If they wanted to make me hate her, they sure did it.
As for the dub, I'm quite the opposite. I enjoy both versions from KOS-MOS (Bridget Hoffman here, not Megan Hollingshead), and some characters are way better in English (Jin Uzuki, Allen Ridgeley, Wilhelm...). The problem was that they had many problems throughout the series, so the best dub is in the last game.
Overall, Xenosaga had a good plot, but Monolith never managed to deliver it in a nice way. The series lost many fans along the way, they had many production problems and in the end the series didn't turn as good as it could have turned out to be.
On a side note: ES Reuben and ES Dinah are just too delicious!