And quite done a couple of full rooms with it, without receiving damage...but where rooms only with wolves and jellys, at the most...never ever thought about using one against goblins. As what i saw, wolves and jellys stay enough time preparing their attacks to actualy stay in the area of the explosion, and wolves simply rush towards them, as jellys pass it, and them attacks backwards, simply falling into the explosion. Well, it's good when you have some room to run, and the monsters aren't so hard, but numerous enough to make some damage.
Bombs could really bee imprved if the explosion had a duration time, like 2 seconds, and not a instan explosion, so, if the monster is coming to you, and the bomb explodes beforehand, the monster would still receive damage, if he continues to walk to you. Also, there could be non damaging bomb explosions that only gives a huge knockback, and stays longer (think of it as a savior barrier when you need time to drink that pokeball, or to actually drop a powerup without being attacked).