I think it's smart, fun, hilarious at times, and doesn't give a fuck on a scale so grand it's almost poetic. I don't think anyone ever asked, during the course of development, if anything made sense or not. The only parameters were whether it was fun, possible, and if they had time to put it in. I think the movement is actually better than Prototype (to which it is most similar in that regard), though the melee combat is no better than in SR3. I think the writing is better, for what it is trying to be at this point, than at any previous point in the series. That is to say, it's fucking crazy from start to finish, but more consistent than something like SR2 that clearly wanted to be serious in the main plot, while having you drive a poop truck in side missions. This game is crazy and it means it, and it's not going to compromise that insanity by having anything serious or dramatic intrude at any point.
It's not perfect by any means, but I loved it. It wears the signs of it's origins as a DLC gone rogue very clearly, but I just don't care. I have no idea what Volition is going to do next, but I hope they don't lose this sense that, somehow, you're playing something generated by actual lunatics.