I currently run a D20 D&D Forgotten Realms campaign and I will be playing in a D20 Star Wars game, starting this wekend. I also like the look of Hordes, but I have not picked up the rules yet, but I do have the makings of an Everblight army.
As too why I play the games I do, its because, I am a fan for both the Forgotten Realms and of the Star Wars universe, plus my game group are also long time D&D and Star Wars fans. I think both games are simple to learn and are very enjoyable to play.
I have also in the past played d20 Judge Dread (I am the law!) which was a blast and a home brewed 40k roleplaying came, which was based off of WFB.
I have played the Star Wars CCG, from Decipher, what a fun game that was. Magic the Gathering, impossible to keep up with all the new cards although it was fun for a while. I have also played the Raw Deal ccg, which was fun to play when I was a fan of the WWE. Now I just can't get into it.