Yes and no. In my experience, the Unclean Beast is a fairly easy to play melee character. Furthermore, the unclean beast tends to do quite well against players who are inexperienced. As a result, n00bs will gravitate towards the unclean beast since it is a simple and powerful melee character with loads of damage spells that excel against players of lesser experience.
However, many experienced players can find ways around the Unclean Beast. One of the unclean's most annoying spell (Venom Spit) deals damage over a period of time to avoid this you can do any of the following:
Sedna can be played to stack health to the point where she will still heal even with Venom Spit.
Erebus can use his Mist to immediately remove negative buffs.
The rook can tower spam so that The Unclean Beast can not even get close enough to use Venom Spit.
Oak can turn invulnerable.
QoT can use the Bramble Shield which will automatically take the damage of Venom Spit (even if the venom spit buff was already in effect)
...and these are just some of the examples.
When my LAN group first started playing this game, the unclean beast was impossible for us to beat because none of us would buy items or use intelligent strategy. After you become used to the game, you find out that the Unclean Beast is a great pain in the ass in the beginning of games, and can be harsh to play against even when a n00b player plays the character, but in the end, the Unclean Beast can be defeated. And if you can survive until the end of the game and are wise with your abilities, you can p0wn the thing.
The advantage of the unclean beast is that any n00b can play as it. The disadvantage is that it is only as good, if not worse than experienced players playing as other characters.