Xenosaga was a greatest hits game, but I think them botching the second game is what killed the sales. I still can't bring myself to play Xenosaga 2, and because of that I still haven't played or bought 3 either.
To be a greatest hits, you need to sell 300k in the US. Less than that for Japan's The Greatest line.
The original game did sell fairly well (400k in Japan and around 300k for the US since it was a GH, 700k overall). But the subsequent games were poor in sales. 200k for Japan, less than that (IIRC) in the US, Xenosaga 3 did about the same.
Back on the subject, I like Sazh, he's a total Red-Mage type of character. He gets Haste, Bravery, Faith and more for the offensive line. Later on he'll pick up the defensive stuff that Hope has like Shell and Protect. What's even better is that he also gets the En-spell line, which means if he's in Commando, he can use the -Strike line of spells found in Ravager and fight pretty decently as a Commando. He's also not too shabby as a Ravager and has the typical stuff found there. He's not going to maximize Ravager like Hope and Vanille, though. Nor can he duke it out with Fang or Snow, but he's well rounded, like Lightning. Though Lightning's more 'paladin' oriented (High Commando, High Ravager, light healing).
Fang's a total Dark Knight. Extremely high offense, and some really interesting Saboteur-spells (like Slow/ga and Curse/ga). I wonder if she'll get Imperil like Vanille down the line. It would make her extremely deadly in combination with Lightning and Snow.