(spoilers)
There's so much to love about Vincenzo: the acting, the killer music, the comedic moments interspersed with intense drama, the action scenes, the contemplation on good vs evil and the nature of justice. Song Joong Ki is at his peak in this drama, making the titular character shine in all his complexity and moral ambiguity. He makes the show what it is and continues to prove that he is a force to be reckoned with on the screen. Jeon Yeo Bin was a new face to me, but I was in love with her within five minutes of meeting her. She's unlike any FL I've seen in a Kdrama to date, and Jeon Yeo Bin masterfully captures her playfulness, her deep determination, and her messy morals. Taecyeon was a brilliant villain, even if his star started to fade a bit toward the end, and Kwak Dong Yeon (another new name to me) stole every scene he was in with his fantastic acting and the complexity he brought to what could have been a very forgettable role as the younger Jang brother.
I do feel that the writers were a bit too generous with Vincenzo. A tight plot and story is all about balancing characters' wins and losses, and quite frankly Vincenzo got a few too many wins. Song Joong Ki did a stunning job with the script, but there was certainly room in the second half of the show for more setbacks, more give and take between Vincenzo and Jang Han Seok. When the protagonist is constantly outsmarting and outmaneuvering the supposedly terrifying, psychopathic villain, it's easy to get comfortable and lose some of the momentum built early on. Jang Han Seok and Choi Myung Hee, both incredibly compelling villains early on, were readily admitting they were no match for Vincenzo well before the end of the show, and failed to anticipate any of Vincenzo's moves or even have much of a plan of their own beyond reacting to whatever he threw at them. I wanted to see Vincenzo really, truly threatened, to see him defeat a powerful villain after a grueling and satisfying battle, but instead, in his own words, he was the cat and Jang Han Seok/Choi Myung Hee were the mice. (For example, for seemingly no other purpose than pissing Vincenzo off, they murder his mother, and are then shocked when he of course retaliates immediately and brutally? How did that murder fit into their larger plans? Why do it at that moment?)
I have other little qualms with the story of course, but overall this was an addictive, intense, entertaining drama that I would definitely recommend for Song Joong Ki and Jeon Yeo Bin alone. If you're looking for morally gray characters who fight evil with evil, or if you just want a fun, action-packed, edge-of-your-seat story, this is a must-see.