I kind of disagree with this. I feel like I know Greg pretty well. I may not know who he is dating, or where he lives, but I think I know his basic character and what motivates him. He's likable, a little off beat, very smart (although I think the writers have often forgotten this); he likes mystery and is intrigued by Vegas history; he became bored with just being in the lab, and wanted the challenge of being out in the field (but I don't think he dislikes being a lab rat at times if it helps in solving a case). He wasn't a jock (lol), and enjoys music and the company of his friends, especially Sara. We know his background, really as much as any of the characters. I love how he gets excited when he knows things that others don't, and when he contributes something in solving a case, even a little detail. And, he takes pride in the fact that he has advanced to a level 3 CSI, just as Nick is proud of his Asst. Supervisor position.
I think when Sara left, we saw a little more maturity in him; he was actually miffed at Grissom (his mentor who usually intimidated him), and he was not afraid to show it (in You Kill Me).
I think often times the lines get blurred regarding character development, a story arc, a character-centric episode, and overall screentime; screentime being more of a contractural thing.
All that said, Greg is due for a character-centric episode, and a good story arc, but I like his character development so far. I think it's seemed very realistic.