My main sticking points with Rupp:
1. His level of competitiveness relative to the world's best is not reflected in his medal haul. Yes, he has two medals from the big one -- the Olympics -- but he never once medalled at any other global championship (Worlds, World Indoors, World XC, etc.). Bernard Lagat, Paul Chelimo, and Nick Willis all have an Olympic silver and a bronze as well, but all of them won at least one other global medal. Now, Lagat is one of the all-time greats, but Rupp is certainly better than Willis and Chelimo in terms of pure talent. Additionally, his range is vastly superior to any of the others I mentioned. Just look at his PRs, which an earlier poster listed. Nevertheless...
2. Those PRs are still not wholly representative of his ability. The mile and 10k times are, I believe, in line with the fastest he was capable of. Additionally, his former ARs in the indoor 3k and indoor 5k were great times at or close to his maximum potential; his current AR in the indoor 2-mile is truly extraordinary. However, in the outdoor 5k he never ran as fast as he could have; he clearly had AR ability and could have run sub-12:50. Likewise in the half marathon, he could have easily lowered Hall's mark by 30 seconds or more (even now, if he really ripped one with lots of healthy buildup behind him, he might still be able to challenge the record). His marathon time, as he himself acknowledges, should also be faster. If Cam Levins can run 2:05:36, Rupp can still -- or, at the very least, could have -- run 2:04 (I do think the marathon is Levins' best event by far; he can still PR again, and he might end up being better than Rupp). Rupp is, after all, clearly a better marathoner than his former training partners Farah and Osako, yet they have quicker PRs.