Spartan X/Kung Fu Master/Kung Fu:
(Arcade, Atari 2600, Atari 7800, Apple 2, Commodore 64, Amstrad CPC, Micosoft MSX, NES; 1984):
Button 1/B: Kick
Button 2/A: Punch
Up & 1/B performs a jump kick, Up & 2/1 performs a jumping punch(probably more useful in stage 2, if it has any use at all), Down & 1/B low kicks, & Down & 2/A low punches.
The game takes place in a 5 floor temple, with each floor having it's own guardian, and the even numbered floors having different enemy types(stage 2 mostly has falling orbs you need to watch out for, but can easily destroy when within range, that can turn into snakes that can't be fought, but then must be jumped over, or dragons, which can be defeated if close enough. If the orbs don't just hang there until they eventually explode, in which those can be dealt with a jump kick. Stage 4 has moths that fly at various heights). After you defeat the final boss, Mr. X, the game starts you over again in a harder difficulty, like the classic arcade game that it is(The Donkey Kong series is the fist to come to mind as games that do the same thing). It's obviously a little easier, in the NES version anyway, than the arcade original.
Enemies in the even, and very ends of the odd, stages include the generic goons, who if they get close enough, will grab Thomas, your playable character, and drain his health. More enemies can then grab those enemies and drain your health faster. Just mash buttons/directions to get shake loose. Knife throwers are the bigger threat, not just for the range of their weapon, but the fact that they take 2 hits to put down instead of the usual 1. Toward the end of the 2nd stage you'll be introduced to small enemies. In later stages they try to somersault onto Thomas' head if you're crouching, but this can be beaten with a simple jump.
The game is very loosely based on a Chinese martial arts film starring Jackie Chan, which was localized as "Wheels on Meals"
Depending on how you look at it, some wouldn't even consider this a beat 'em up. However, this is the first side scrolling game in which you control a martial artist who must fend off waves of multiple opponents, and quite frankly, the player won't get far if they don't stop to fight. In that regard, this game can be seen as the progenitor of the beat 'em up genre.
Spartan X/Kung Fu Master:
Game Boy (1990, original Japanese release)
The controls are literally the exact same as the NES port of the arcade game. The one exception is that there's a backflip kick, that I'm not sure how to pull off(if it's even something you control, like the way reverse attacks are automatic in the 16-bit TMNT games). Though, to be honest, it doesn't seem to be all that useful.
Differences in gameplay include the fact that you're traveling in more outdoors locations, have more than 5 stages/bosses, can pick up items, and new enemy types. The items are usually health restoration, sometimes dropped by enemies, but can also include bombs, which are used by the A button(there's an indication by the letter "B" showing up in the middle of the bar next to the lives counter). Tougher enemies, unlike the knife throwers in the previous game, can take ~5 hits to put down. The game also gives players 5 continues, instead of a game over after losing 3 lives. Later stages also see more hazards and platforming, so you'll definitely be needing those continues before you have the game figured out.
When you defeat the final boss, you get an ending, and you're brought back to the title screen. That makes for a short game, but it is for a handheld with limited battery power.
Spartan X 2:
Fan Translated as Kung Fu 2: http://www.romhacking.net/translations/659/
The controls seem to be the same exact as the NES port of it's predecessor.
This one borrows some ideas from the Game Boy game, like the health resoration items that often drop from tougher enemies, and traveling around outdoors, with finite stages with an ending. It also has a lot more presentation/story to it.
There's not much else to say about it, as it's still as simplistic as these games get. Though your playable character and the bosses have a lot more durability, so boss battles will be a lot more of a fight in this one(not that they weren't much of a fight in the others).