Let's skip past the tropes of explaining how darkness affects everyone differently and our own adaptations to the dark and get right down to how can we use it to murder as much shit as possible.
The Prototype games are...ok. They're messy and hard to control, and tons of shit
is going on all the time, especially in the second one; but, there are some damn dark and sinister stuff you can get into. Let's gloss past the fact that your arms turn into massive blades used for slicing anything, and take a look at the achievemenets.
Even if you think you are going to be somewhat of a good little hero mutant thing...you're not. This game was designed for you to take that darkness inside and just let it out. Achievements like Consume 200 Characters, Run over 500 Characters in a Single Tank, and my personal favorite, Patsy 5 Military Personnel. Yes, you get an award for blaming some poor idiot of killing his comrades, and then they themselves are essentially executed. Delightful.
So, darkness isn't the option here, it is the entire point. Much like the Venom movie that seemed to "borrow" a lot of the ideas from this game. No matter what you do, you're going to end up killing A LOT of people. Embrace the darkness.