Prior to '08, Greene had to get his grades in order at Kirkwood. He also had ballooned-out in terms of weight ... I remember some folks claiming that he had gotten up to 280 ... but I think that it was more likely that he was at around 260 to 265. Thus, he came into the season lacking conditioning. Furthermore, having ballooned-out like that ... he lost most of the high-end speed he had when he was younger. However, the flip-side of that is that he had great balance and toughness ... and he really ran behind his pads. When you run behind your pads, keep your legs driving, and you have good balance ... it can be really tough to get you down.
Anyhow, as you indicated ... Greene was great at reading cutbacks in Iowa's zone-system. He'd see an opportunity, and make the cutback ... and then just run hard. There were obviously broken bodies strewn behind (and around) him. You know you're doing something right when you reach around 1800 yards rushing on a season!
Anyhow, I see Kaleb as more of an upright runner than Shonn. Furthermore, Kaleb has higher-end speed (compared to '08 Shonn). However, Kaleb has the similar attribute of having pretty good vision and reading his blocks. Perhaps due to his upright style ... he's able to "get skinny" and make it through more narrow holes than Shonn. On the flip side, it's obviously significantly easier to bring down Kaleb than it was to bring down Shonn.
The comp that keeps on coming up in my head when I watch Kaleb is Adrian Peterson. I see the comp to Melvin Gordon too though ...