I'm a relatively (five games) new player using Marcus as my first master. While it's quite possible to play a variety of styles with Marcus depending on what animals you bring, I play him because of his speed and I bring speedy models with me. I love that I can play most games by focusing on objectives rather than just killing my opponent. Marcus himself is great because his Wildheart ability allows him to be excellent at one thing at a time. I tend to use the speed and Df boost to get into position and let the enemy come to me. Then I boost Cb and to damage put the hurt on whoever dares approach me.
Lack of attack power is Marcus's big weakness. Most of his minions either don't hit hard enough or don't last long enough to continue to hit hard. But I've loved the challenge of learning to play the game without rushing into combat.
Visual unity really isn't so hard. Avoid the bright colors of the Marcus box set art and you'll be fine. Once I find time I plan to have mostly dark blues, purples, and grey in my paint scheme. And remember, he's getting an alternate model so if you wait, you may find that one more to your liking.
I recommend some of the Marcus diaries to get you excited and to learn more about his playstyle.