I didn't hate the old SD v RAW series, but to ignore that some changes were needed would be to ignore reality. WWE 12 was a solid first attempt at revamping the series and WWE 13 further improves the overall plan.
WWE 13 is carried, largely, by its storyline. It covers the Attitude history, from the creation of D-X before Survivor Series 1997 thru WrestleMania XV. OK, a further storyline you unlock goes a bit longer, but has no actual core storyline, so it doesn't really count, does it? You have to work through the rise of D-X, followed by the rise of Steve Austin, the UT/Kane program, then we have Mankind and the Rock stories. All are as good as Vince Russo's notoriously terrible writing allows them to be. The final one you unlock covers specific people, such as Lita and Trish.
The game controls well and some of the additions are nice. I would recommend playing as CM Punk as you get the benefit of most of the new, small additions. You can now catch guys like Rey or Sin Cara and hit your finisher on them. You can taunt them to get up --- and then hit your finisher and win. The gameplay seems slightly more fluid and organic, which I do like as an improvement. Heck, this is one of the few games where the Achievements/Trophies are helpful because I wouldn't have tried either of those things if not for getting an Achievement for doing it. Once done, I actually did use it regularly.
There aren't a lot of other tweaks, but the core part of the game is solid to begin with. I do like WWE Universe mode. Some of the feuds they program you into seem silly, however, you can just change them if you do so and end the ones that are just not working. The customization is still a significant benefit. You can customize almost anything. Kicking out of pins is terrible (way too timing intensive) and the AI is either going to kick out at 1 or get pinned. But it really is a minor criticism. The pinfall mechanic doesn't come into play a ton, mainly because the game just isn't that hard. Even on "Hard", it isn't all that brutal.
Online is a problem as usual. THQ has not pulled off online well with the WWE series, so that tradition remains strong. You will lose connection too frequently for comfort. I didn't get the game for online play (largely due to the history of it not being great), but if you are looking forward to fighting your friends online, you can likely drop a star off of this rating. It will work well sometimes, but will be a headache just as frequently.
WWE 13 is a good game. It is worth your time. It is worth playing. If you like the WWE, it is a definite. If you don't like wrestling, then maybe not.