Combine the 2 or more games to come up with a new improved game. (you can also pick a snazzy name for it) For Example Xcom plus use the battle system from jagged alliance.

Strip-Jack-Naked Snap is better than the sum of its parts.

Strip-Jack-Naked is that card game where you deal out all the cards to the players and each player plays 1 card at a time (from the top of their pile, you can't pick which cards to play or see what you have got), unless a JQK or Ace is played, in which case the next player has to play 4 cards in turn (for an ace), 3 for a king, 2 for a queen and 1 for a jack, if they don't get another J-A they lose and the person who played the card takes the pile. If they do play a J-A, its the next players turn to try and play a J-A. The rules mean that if you knew the deal of the cards you could predict who was going to win... but combining it with snap is the bees knees.

[EDIT: the winner is the player who wins all the cards]

The open gaming environment of Hitman, the graphics of Half-Life 2 and the setting of Syndicate. *drools*

The graphics and physics engine of the Pro Evolution Soccer series combined with the A.I. and management style approach of the Football Manager series.