I thought the first one was solid, but just plain grim. The sequel is better in every way, and is possibly the best non-GTA/Witcher open-world game I've ever played. Mechanically and graphically, it's great, the side missions are great, and there's a real sense of freedom to finding your solutions. The only technical issue it has is some laughably bad voicework in places.
I do have to agree with a couple of the reviews, though - a no-kill playthrough is really the only thing that makes any sense given the plot/characters. One of the reasons that the first game was so grim was that you faced consequences for killing. Killing civilians and cops would damage your reputation (a mechanic that I'm kind of happy is gone, since it was damned hard not to run over a civilian every once in a while), and Aiden Pearce's propensity for shooting all of the bad people basically lost him his family. Marcus, on the other hand, is just a goofy, happy-go-lucky guy, and remains so even if you kill 30 FBI agents on your way toward stealing a van. I am happy that it's possible not to kill anyone, though. Ridiculously hard at times, but possible.