If you have a Spirit of the Forest (with protect) on your green team, everything becomes much easier! Flesh Golem makes a great tank, especially if he has void. Also, if Swamp Thing is powered up enough to have 'slow', your team is pretty much unstoppable!
Well maybe not unstoppable... but with weaken (-1 health) and slow (-1 speed) on your enemies, and protect (+2 shield) and health bonus (+1 health) plus double healing for your flesh golem... tough to beat!
I tag @monsterplayer for a card.
HOLY SHIT... Just checked out Spirit of the Forest... and nope... don't have one of those yet.
The rest of the monsters though DO become a lot more useful as they level up, yes... but the other colours are useful at levels 1 & 2 already (which is where I'm playing around at the moment).