I don't hate Cena, either, but sometimes when you over-push something, when it's jammed down your throat, it can get old. Sometimes it sounds better if a heel has a long title reign because people will eventually get tired of him. I did watch the Last Man Standing match between Umaga and Cena, and I have to say I wasn't too impressed either. I compared the Last Man Standing match of Cena/Umaga and Undertaker/Batista, and although both matches have completey different roles for the wrestlers, the quality of match was very different. Results aside, there's a difference in how the wrestlers fight in the match, and the roles they play afterwards.
First off, in the Cena/Umaga match, there was NO QUESTION in my mind who was going to win the match. I knew that somehow Cena was going to win. He was playing the underdog role to Umaga's unstoppable monster, which is a tired schtick in itself. It's the role of absolutely beat the hell out of the champion/underdog, and he has the fortitude to get up and fight back and get the hard fought win. A Last Man Standing match with Edge would have been more interesting, since both men are even in size and the match could have more evenness. Cena/Umaga was basically a Hogan/Andre re-make, and while the loose rope STFU was creative, it was almost out of place. It seemed pretty random and not in a good way. Good match, not great, not one I'd watch over and over again. Meanwhile, Undertaker/Batista, despite being a HUGE Taker fan, I still had no true idea that Taker would win (it ended in a draw, though, which no one liked or wanted). Still though, the psychology of the match was interesting because you had frustrated former champ against a wrestler who can play any role in Taker. With the Undertaker's matches against Batista (who I am NOT a fan of at all) he put together three intense back-and-forth matches that no one had a real idea of who was going to win. If Batista were to turn heel now, it would make complete sense since he had the bitter loss and two straight draws to Taker then the two losses to Edge. This was propelled by Taker. I would watch Undertaker/Batista's Wrestlemania match over and over again. It left me out of breath and excited when he won.
Did Cena really help put over Umaga or Khali? How many people actually thought Khali would beat Cena? Or Umaga? What happens to them now? After beating Cena to a pulp and losing twice, Umaga was Vince's wrestler/bitch for the Donald Trump angle which led into the Bobby Lashley feud, but it wasn't even for the ECW title. Sure, he was Intercontinental champion, but did that actually help him? Not like he was a great champion since he defended it maybe three times total. Why put him in a feud with another top champion and never even have a chance at it? As for Khali, now what with him? He's been pinned AND he's tapped out to Cena, so where do you put him now? Who do you put him against except maybe Taker again so he can finally pin him? It seems like unless you change shows, after losing to Cena you're kind of in career limbo. And how many of the matches with Cena and Umaga OR Khali would you want to watch again and again? As for Cena/Shawn Michaels at Wrestlemania, the match just seemed very off. Their RAW match was a little better, but not by much.
Out of Cena's history in the WWE, I can think of three matches he had that I was impressed with: the TLC match with Edge in Toronto, which had the sneaky heel champ vs. frustrated champ roles, and I was very impressed with both men; Cena's Wrestlemania match with the Big Show for the U.S. title, because it was where Cena began the beat-down underdog role, and he played it well against an aggresive Big Show, and the Cena vs. Rob Van Dam at One Night Stand 2, because Cena absolutely EMBRACED the heel role he was playing, and was such a good sport and professional, and the match itself was so incredibly intense.
Just my opinion, though...not out to criticize anyone but putting in my 5 cents...