Master System games

Batman Returns -- Platformer title starring Batman. Cool grapple hook mechanic, two difficulties, neat, tough level design. Well worth playing.

Sonic The Hedgehog -- The 8-bit counterpart to the Genesis title. It shares some of the Genesis version's themes, but is still a completely different game. Emphasis on platforming instead of the "Gotta go fast" nonsense the series has turned into.

Sonic The Hedgehog 2 -- Came out before the Genesis version, interestingly enough. Made by different devs, so the physics are a bit different. A lot tougher than Sonic The Hedgehog.

Sonic The Hedgehog Chaos -- Very easy Sonic game, but enjoyable nonetheless. Introduces the spindash and peel-out mechanic. Great music and fun platforming.

Castle of Illusion starring Mickey Mouse -- Shares the same themes as the Genesis version, but has very different level design. Mickey's girl has been captured by an evil witch and it's up to Mickey to rescue her.

Lucky Dime Caper starring Donald Duck -- A surprisingly tough platformer game. Tricky, but well-designed levels make it a challenging, fun game. Donald's nephews, their lucky dimes and Scrooge's lucky dime have all been stolen. Donald travels around the world and traverses many cool, themed stages as he tries to retrieve them.

Asterix and the Secret Mission -- Though a rather easy game, the charming music and level design make it very enjoyable. The game does suffer from some lag issues, but don't let that deter you. Play as either Asterix or Obelix as they collect herbs for their magical potion and punch Romans on the way.

James Pond 2: RoboCod -- An extremely European game. You control a half-robot fish, as he tries to rescue Santa from Dr Maybe's nefarious plans.

Master of Darkness -- It's essentially the Master System equivalent of Castlevania, except better.

Dragon Crystal -- A very unforgiving, but awesome roguelike. You control a boy who one day finds himself in a magical world filled with monsters. Fight your way through 30 floors to recover the titular Dragon Crystal and go back to your own world. Game is extremely random and tests your ability to adapt to the limit.

Ninja Gaiden -- Though it's an 8-bit Ninja Gaiden, it's nothing like the NES games. This game is very fast paced and focuses more on tight platforming next to combat.

Bonanza Bros -- Much more extensive than the Genesis version. Sneak your way through 10 levels as you steal various kinds of treasure. Starts off easily, but gets quite tough near the end.

Phantasy Star -- The first game in this awesome series. Though a bit grindy at times (as every RPG was back then), the cool story and combat make up for it.

George Foreman's Knock Out Boxing -- One of the best fighting games of all time #Kappa