Skill Text: "The rarest of arrows are perhaps also the most powerful ones. Extremely dangerous in the hands of some bowstring-happy pyromaniac – and absolutely frightening in the hands of a skilled archer – these arrows explode upon impact: not only turning the original recipient into a bloody jigsaw puzzle, but also tearing apart anyone caught near the blast."
While Explosive Arrow may look underwhelming at first, take note of how quickly the radius increases and the fact that the damage scales with Heightened Reflexes. Once a character has gotten to a "moving on to the flying fortresses" level of power, it's not uncommon for Explosive Arrow to have a 50% chance to crit the entire screen for ~3,000. Also note that the explosion radius ignores line of sight and solid objects, meaning launching a high level Explosive Arrow into a room may very well hit enemies in another two rooms through walls... and with a cooldown as short as 5 seconds and a cost as low as 67, the skill can nearly be spammed (even by a character with low Spirit or Mana Regen).
If you max out one skill as a bow-user in the original game (Ego Draconis), let it be this one. If you hunt down skill points thoroughly enough to make it two, pair this skill with Fireball (which follows the same mechanics, ignoring solid objects and doing plenty of damage regardless of available weapons). Even with level 28-30 enemies, an entire battlefield can be leveled in 5 seconds by opening with Explosive-Fireball-Splitting-Explosive.
If playing all the way through Flames of Vengeance, there are FAR more skill points available and much better options for guaranteed good bows, causing scaling issues later on. Far stronger enemies and Fireball/Explosive Arrows becoming relatively weak combine to make them a bad choice for the expansion. Consider maxing Splitting Arrows.