The reason I chose this game is because the majority of people that get Callus, do so mainly for the Street Fighter II series, and they often overlook the other games.
This particular game is an all time favourite of mine because it is actually 3 entire games rolled into one :
For the Shoot-em-up fan theres Chariot which is a side scroller much like R-Type and has all the elements of a good shooter, such as big powerups and huge bosses.
For the Platform fan theres Midnight Wonderers which in a way is a little like Contra where you control this elf-type guy that progresses throughout the level with a big boss at the end of each. Along the way, you can pick up better weapons and heart-cards which act like coins in the Mario games.
For the puzzle fan theres Dont Pull which is a homeage to Pengo, the old arcade classic, that sees you pushing blocks against walls to crush the enemy.
What makes all of these games fun to play is that they all have a simultaneous 2 player mode, where a friend can join in the fun. I urge everyone to try it out, since out of the three games available on it, at least one will be liked by everyone. I personally love all three of the games, and often play Midnight Wonderers until I finish the bugger.
This is a total classic, so stop reading this and go hunt for it. You will not be dissapointed.