Two volumes is in no way sufficient to explore this kind of serious premise in-depth, so it's not the thought-provoking psycho-thriller it could have been, but for their length, all the stories (there are four sets of characters and situations, each with very different circumstances and outcomes) are clever and psychologically twisted enough to entertain.
The only thing I found slightly off was how quickly and on what flimsy grounds the 'contractors' accepted Mikuni's terms and conditions, considering the gravity of the acts they were about to commit on her word. (Perhaps this could be put down to muddled thought processes in the wake of overwhelming emotion, but...) It contributed to my rating dropping a bit, but apart from that, Murder Incarnation is a fairly enjoyable (for want of a better word; it isn't the least bit fun, obviously) and atypical read.
The art is odd. It's certainly creepy enough to match the mood the plot sets, but the frozen expressions dulled the emotional impact quite a bit. Still not grounds to avoid reading, though.
Another thing to note before taking this on is that the first story is the weakest in terms of both plot and characterisation; if you find it underwhelming, I recommend reading the second one (chapters 3-5) before deciding whether to drop the manga altogether.
I especially liked the plot twists: believable in hindsight but very difficult (though not impossible) to predict. If you like surprise endings and don't mind a high body count, this is for you.