What interesting about the Castlevania games for the Nintendo 64 (Castlevania 64 and Castlevania: Legacy of Darkness) was how many ideas they threw into the games. Originally slated to be one game before deadlines forced Konami to release the first version (Castlevania 64) before it was totally done, the two games feature multiple characters each with their own full quests, differing storylines, and unlockables, all while building it on a new system with an engine completely different from anything that had come out in the series before. It certainly didn't lack for chutzpah.
Just take Henry, for example. Although not one of the original charcaters first teased in pre-release articles for Castlevania (those focusing largely on the characters that would eventually become Cornell and Reinhardt), Henry was included as a bonus mode in Legacy of Darkness. Because that game was a kind of prequel/director's cut hybrid, Konami decided to focus the main storyline on Cornell (who had been cut from the first version of the game). Henry was then thrown in as a way to unlock all the other modes and bonuses in the game with a mode completely different from the other characters -- you weren't concerned with defeating Dracula but just rescuing kids (evoking shades of another classic Konami game, The Goonies).
Think about that from the perspective of the games that had come before. We'd had multiple characters, sure, but in games like Castlevania III and Dracula X the characters followed the same paths, had the same stories. In these games, though, each player had their own motives, their own levels, their own stories, and even their own modes. As good or bad as the game may have turned out (we at the Inverted Dungeon like them despite ourselves) the game really did try new things and go in directions that, in some ways, were never really explored again.
Prior to Castlevania: Legacy of Darkness
As hinted about in Cornell's story in Legancy of Darkness, Henry grew up in the Oldrey Villa along with his mother and father. Unfortunately for the family, the lands of their home were encroached on by Dracula's evil magic (whether it was always part of Dracula's lands and the family just moved in and built a home withb a terrible location, or if the house simply was consumed by the darkness over time, was never made entirely clear). This eventually lead to the forces of darkness invading the family's lands, attacking the father, and turning him into a vampire hell-fiend (who are much more into drinking blood than normal hell-fiends). Henry and his mother each tried to find a way to safety, but the forces of darkness had other plans.
Castlevania: Legacy of Darkness
Thankfully (at least for Henry) a werewolf hero came calling. Cornell (aka Blue Cresent Moon to his friends and colleagues) was on his own quest in Dracula's lands, desperately searching for his kidnapped sister. Upon arrival at the villa, Cornell engaged in mortal combat with the man of the house, the vampiric Lord Oldrey. Oldrey had been attacking the door to one of the bedrooms, trying to get through the barrier the mother had constructed to keep him out (since the father had desire to drink her blood and, of course, kill her, something she was seemingly disinterested in). Cornell dispatched the vampire, freeing the woman, but she informed the werewolf that her son was still lost in the grounds somewhere. She begged him to find her son while she (for whatever reason) would stay in the villa to await her fate.
Exploring further into the grounds (as much to find a way into the castle proper as to find the boy), Cornell stumbled upon the young Henry fleeing from a onstrous autonomaton/well-paid gardener (a kind of Frankenstein's Creature but with better, and more specific, training). Cornell helped the boy escape the beast, saving his life. Cornell told the boy to follow the path out to safety while he, Cornell, would venture further into the castle to save his own sister and free the lands of darkness. As it turned out, though, Cornell was only able to do one of the two things -- though he and his sister escaped, Dracula's magic took a stronger hold of the lands around the castle, a problem that would have to wait for future heroes. Safe from the grounds of Dracula's castle, Cornell, his sister Ada, and Henry left to find peace and new lives out away from the darkness of the demon prince.
As it turned out, though, one of those future heroes would end up being Henry Oldrey. Eight years after fleeing his family's home, the young man returned. Having spent the intervening yuears training as a knight of the church, developing skill not only with vampire hunting weapons but also fire arms. After hearing that children were being kidnapped from villages nearby Dracula's castle, Henry venture into the grounds. Knowing that others would go into the castle to defeat Dracula (specifically Reinhardt Schneider and Carrie Fernandez), Henry focused his efforts on finding the children and getting them to safety.
Exploring the grounds of the castle, Henry was able to find, and free, six of the yound children. He helped them escape, getting them safely back to their family. Sadly he did miss one child, a yound boy named Malus who would go on to become the vessel for the dark lord...
As noted, Henry doesn't hvae a normal adventure in the game. Instead of exploring Dracula's castle fully all on his way to defeating the Dark Lord, Henry explores each of his six levels looking for a kid to save. Once saved, Henry is done there and can just move on to the next area. It's an unusual mode for a Castlevania, one often critisized for being a little "under cooked" since Henry doesn't get any real cut-scenes and bearly has an ending. Still, playing through Henry's mode is the only way to unlock all the other bonuses in the game (like Reinhardt and Carrie's stories).
Playing as Henry:
Henry was resoundly mocked by fans during the initial release of Legacy of Darkness because he was a knight in shining armo that carried a big freaking gun. Seriously, a gun was his primary attack, and oddity for a series that hadn't ever had firearms in it before (and then shied away from them entirely until the games moved into the future with Aria of Sorrow and Dawn of Sorrow (and in those games they were well hidden or double-secret unlockables). It was just such a big shift for the series most fans though it was silly.
Still, despite the way it looked Henry proved to be a capable fight much like the rest of the heroes in the game. His gun served as his more powerful attack (a la Carrie's force orbs or Reinhardt's whip) while he also had the standard melee attack as well, a long dagger. And, of course, like everyone else in this games, Henry could use sub-weapons. Maybe the issue was that he just wasn't different enough to stand out from the other characters -- take away the gun or the armor and he would have blended in a little too well with the rest of the crew (to the point where one has to wonder if his inclusion was really necessary at all).