You don't have to be over the top but you certainly need to be energetic. At times even when I'm at my most energetic state I can sound monotone and that just happens, it's pretty much how I sound when I talk. You also have to factor in the type of games you're playing, if you're playing fairly mundane games or games with almost non-existent action or basically games that don't have a lot of stuff happening, it can effect how you react, talk & play.
Mr Sark, SeaNanners, Two Best Friends Play aren't over the top gaming channels but they certainly have a positive energy about themselves that resonates in their videos. So you definitely need energy at the very least.