Greg Oden's rebounding is what sets him apart. If his rookie year is any indication, he is a once in a generation offensive rebounder.
According to basketball-reference.com, his rookie year offensive rebounding percentage was 15.7%. This is right up there with the rookie years of Rodman (15.6%) and Moses Malone (15.5%), and above Buck Williams (13.7%) and Barkley (12.5%). These are generally considered the greatest offensive rebounders in the last 35 years.
Dwight Howard led the league in offensive rebounds this year by a far cry, and he had 13.8%. So Greg's offensive rebounding rate was 14% better than this year's league leader.
This manifests itself not only as an individual stat. In fact, he not only grabs more offensive rebounds when he's in the game, the whole team grabs even more. So he doesn't "suck up" offensive rebounds from his teammates. Rather, he "makes his teammates rebound better" (related to "makes his teammates play better"), and to an amazing degree.
From basketballvalue.com come the team offensive rebounding stats. The average team has an offensive rebounding rate of 29%. These numbers are fairly clustered, with all but the best and the worst ranging from 26% to 31%. The best (except for Portland) is Philly at 33.4%.
Portland without Oden, is 32.5%, which would be 2nd in league. But with him, we rise far above the pack. With Greg in the lineup, our offensive rebounding rate is 38.7%! If you are into statistics, with Greg in the lineup, Portland is 5 standard deviations better than the average.
For one individual player to make that much of a difference is truly amazing. It's such an incredible margin, and indicates that he is a once in a generation offensive rebounder.