Think it's a bit hit and miss, he can put on an absolute epic if he's put with the right people, the matches against edge, especially the TLC match. Then you have your example which was prominent at Extreme Rules - Brock Lesnar's first official match back in WWE, i'd be inclined to blame Lesnar a bit though too, the guy was dire in that match, he looked like a log after 5 minutes and could barely move. I don't think Cena is the best at carrying a match alone, but again if you get the right guy with him he'll create an epic.
Punk and Edge were two of the best to get Cena looking great in the ring. Remember that piledriver?
