Depends thoroughly on the game. Spades, Hearts, Euchre, already done very well by Freeverse, with nearly all the features you described. Not much of a draw there for me personally.
If there were some lesser-known card games, though, I'd be real interested: Scum, 9 Up 9 Down, some Rummy variants. That sort of thing, you'd have my attention.
Multiplayer probably would top my list. Similar design is not an especially big deal, though it makes sense if you're trying to sell a series of games. Playable with Windows, definitely a plus. Low-cost, nice too of course. Sure hard to find all those things together.
Two cents.