Badass Baritone: While his natural voice is actually a little bit higher than what most people hear, the voice he uses most often is this.
Deadpan Snarker: If his Twitter account is any indication, he's got a killer sense of humor.
Evil Sounds Deep: If the character he voices happens to have a deep voice, then they are most likely are going to be villains. If the villain has a higher pitched voice, then said villain is going to be psychotic.
Heterosexual Life-Partners: With Sam Riegel. Their joint podcast makes it abundantly clear that they're BF Fs. At one point Liam O'Brien challenges them both to pick which male voice actor they would marry if given the option - and the challenging part is that they're not allowed to pick each other.
Playing Inigo from Fire Emblem Awakening, had him playing a suave, happy go lucky, overly emotional, ladies man who was just out to make everyone smile.
He played ShobuKirifuda in the second and third seasons of Duel Masters, AND the young version of the aforementioned Tokugawa Ieyasu in the Sengoku Basara Samurai Heroes anime. That's as far from his usual typecast as one can possibly get.
Played around with Yasuo of League of Legends. The promotional trailer paint him as a cold-blooded murderer, which may look a little in-line with O'Brien's type. When he's eventually released? Turns out Yasuo is an innocent man, framed and trying to seek justice from that, and was a formerly arrogant Samurai that learned the arts of humility for real. Still got the eagerness to fight, though.