Master of Darkness
The Castlevania series has seen it's share of clones and pretenders. It's not hard to see why people would try to copy the Castlevania formula -- the series has seen moderate to great success with most of its releases, and by most accounts the fans of the series rally around the various releases. Being able to get in on that fan furvor is certainly a desirable goal.
However, just being "inspired" by is different from flat out copying the series. The Ninja Gaiden series for the NES took elements of the Castlevania formula to craft a different set of games -- an homage with new ideas is compendable in its own right. However, a game like Master of Darkness simply takes what works for the more famous series and does it again, almost verbatim.
Similarities to Castevania Games
What's obvious right from the start is that, despite an opening stage set in foggy England, Master of Darkness was an attempt to bring Castlevania to the Sega console which, at the time, didn't have one of the games to speak of (that wouldn't come, as it happened, for another year). Exploring fairly linera levels, fighting monsters with weapons and sub weapons, the hero, Dr. Social, is on the case trying to find the evil killer Jack the Ripper. What he descends into, though, is a tale of darkness and evil, capped by a battle with the evil vampire Count Dracula. Literally Dracula, and not just some other master vampire. It's like the developers figured, "people know what we're doing, so why try to hide it?"
So much of the game feels like a direct rip from the Castlevania series, it's almost like they loaded a ROM up and just stole code (not that they did, for obvious copyright reasons). Your hero needs to traverse up and down flights of stairs and while he can jump through them, he can't jump onto or off of them, just like the Belmonts from the classic games. While he's traveling, he'll need to collect items by breaking objects -- not candles but floating masks, but otherwise they are functionally exactly the same. And he'll do all this through a series of levels that would feel of-a-piece with Castlevania -- a gallery, an alchemy lab, and a clock tower all make appearances in the game.
Not everything is directly taken from the game series. As mentioned, Jack the Ripper is a major villain, which is a nice touch and appropriate for the locale. Considering how many horror movies have been made about the monstrous killer, it's actually surprising he hasn't shown up in a proper Castlevania game. Sadly, using Jack the Ripper is the most original of the bosses in the game, and none of them prove challenging or interesting beyond the concept -- simple attacks patterns and meager threats. Even Dracula only have one form in the game, and it's easily defeated in no time.
One other interesting touch is that the hero can gain different primary weapons, like a long cane or a battle axe. These have varying ranges and strengths, so the players will have to strategize which weapons they want to use and when. This inclusion is actually precient considering later games in the series and their expanded, diverse inventories.
As far as Castlevania games are concerned, Master of Darkness is a competent if not creative clone. The best that can be said for it is that it filled a gap Konami hadn't yet managed -- to have a Castlevania game on a Sega system -- and effectively it's the only kind of these games for the Master System or Game Gear. It's just no wonder why a sequel was never produced -- once Konami brought the series to Sega consoles with Castlevania: Bloodlines, why would anyone want a half-baked clone anymore?
Versions of Master of Darkness:
Master of Darkness was released both for the Sega Master System and Sega Game Gear. Like many ports between the two systems, the two games were effectively the same. The slightly smaller viewport of the Game Gear meant the HUD was crunched a bit to fit the screen, but otherwise the two games are, in all ways, exactly the same. If you have a choice, pick up the Master System version so you can play the game on a larger screen.