I really liked Xion and well most of 358/2 cause frankly I feel the Nobodies are far more interesting than the Heartless and the Heart of All Worlds and normal KH shenanigans. So having a title dedicated to them as well as upstart Roxas allowed them to give a few really cool characters better development, which they needed cause I felt KH2 was a disaster of a game in terms of story.

Xion herself pretty much symbolized the main issues of the Nobodies which was that they are not wanted or needed. When they are gone they are gone and Xion took this concept to a tragic end (though coded appears to be hinting that she may actually make a return in the future, as she is actually mentioned in the game, meaning she's not been wiped completely out of existence, and she is one of the people Sora needs to save.) As DEl said, I feel the game really fleshed out Roxas and transformed him into one of the most tragic figures in KH.

Xion herself is not as annoying as I thought she would be and I genuinely empathized and liked her as a character. In truth, she's probably more like a sister to Roxas but I also feel that Namine's relationship with him is not as solid as shipper make it out to be. I always interpreted their words at the end of KH2 to be less romantic and more of a "Hey, we might be Nobodies and we have lost our physical forms, but we're still here". Their relationship never felt romantic, more like they empathized with each other cause they are in the same boat as each other (Abnormal Nobodies that are ostracized by their own kind) so it was more of them sticking together so they weren't alone. The two only spoke for a little while in KH2 and Roxas barely knows Namine.

Besides, I always felt Namine would have more of a thing for Sora himself since he did more for her. Granted the chances of that working was nil but by merging with Kairi she could still be close to him. Though the likely-hood of any of these characters getting major screen time in future installments (beyond coded specifically) is very unlikely, so it's not like any of this will be answered.