Thank you, I have an extra Genesis that I only need cables for. Do you guys think it would be worth it to get one? Are there a lot of card games that I would need?
That's really up to you.
Personally I only own 3 games for the master system and they are all cartridge based.
Montezuma's Revenge (it's the best version of the game ever released)
Wonder Boy (also known as Adventure Island on the NES. The SMS version is better in every way)
Double Dragon (better graphics than the NES version and 2p simultaneous play)
Those three games alone were worth it to me.
Other "must have" sms games I got on "Sonics Ultimate Genesis Collection" for PS3:
Phantasy Star
Golden Axe Warrior
I don't regret not having a card slot yet.
Soera, may be able to comment on the utility of it better.
He has every SMS game ever released.