For five bucks, you could do much worse.
Remember how Dracula loves to take the Belmonts' betrotheds into his castle and having said Belmont get to the Castle, then taking him down? Same deal here. Except that the main character is named Kale and the Vampire is named Ritter. The story does pull a bit of a twist later on, but it's no biggie, story isn't the focus of the game, and it's just a means to an end. Curiously enough, you can actually take pictures and place real faces on the character's portrait, to often hilarious results.
Kale has access to two different weapons, an Ice Lance and a Fire Sword. You can switch weapons at the tap of a button, and each one has it's own combo and magic attack. As previously stated, Magic Attacks are usually used for puzzling, but the affinity of each weapon can sometimes deal extra or less damage on certain foes. Furthermore, defeating enemies or breaking certain objects produces purple orbs that can be used to upgrade your weapons. The game is fairly exploitable on this regard, as you can exit/enter rooms and completely make everything respawn, so that you can farm more purple orbs.
What can one make of Soul of Darkness? It's not terrible, it's fairly functional and at times entertaining, but there's nothing that sets this game apart from other Metroidvanias, it's also fairly short and uninvolved. But hey, for five bucks you could do much worse!
5.5 out of 10