Just completed (the storyline of) this, bit of a strange experience if truth be told. At the start, I'm kinda thinking OK, this game looks pretty average in terms of graphics (kinda like a glorified GTA:SA with much better cutscenes), and the whole shifting thing seemed very bizarre. It throws you into the weird shifting stuff a bit early before you've really got to grips with the game and started to get to know the characters.
However, like the above poster after the first half an hour or so I actually came to like the game. It is fairly innovative, and the shifting works surprisingly well. It even lets them put some variety into the style of gameplay, with some sections that are almost like minigames:
-Protecting an armoured truck from incoming baddies by intercepting them before they reach it (kinda like interactive tower defence)
-Controlling your car from weird angles (chasing car, isometric viewpoint)
-Puzzle section (escaping nightmare on deja vu mission)
The key thing is that once I got past my initial expectation of a vaguely serious game (as was the case with Driv3r and DRV

L), it is actually a lot of fun. The one downside is that shifting ahead of your target to take over an ongoing car and then going for a head-on smash, while fun, will eventually get old and it makes the game a bit too easy. I completed the game in 6.5hrs and don't really feel like going back to attempt Dares, Challenges etc, which I gave up on after the first couple of chapters.
Another side effect of being able to shift is that it basically means there is little point buying cars. I started the game with a Dodge Challenger R/T, and never felt compelled to buy another car as often you hop into others for missions.
Also, while I understand the game can't be taken too seriously, it does feel a bit macabre that you are so concerned about the safety of the city yet think nothing of hijacking a soccer mom taking her kids to practice and slamming her SUV head-on into an oncoming truck at over 100mph. I'm surprised there was room for me in the hospital after the hundreds of accidents I staged.
Overall I'd say this is a good game, the cutscenes and dialog are strong (making some of the chases more interesting), performance is excellent (solid 120fps) and the shift mechanic is quite original. The non-vehicle sections of the last couple of games were pretty weak so I think they made a good decision to focus on vehicles, with a twist. If I had to a pick a game to compare it with, I'd say it is closer to Wheelman than the GTA series. I'd recommend it in the sub £10 price bracket.