Just a game eh, Phil Taylor just won £100,000 for winning a darts competition, he is a millionaire darts player, and so it's a pretty good game eh, how many millionaire shove halfpenny players do you know of, of course it's a sport.
The OED defines sport as "an activity involving physical exertion and skill in which an individual or team competes against another or others". I wouldn't say that darts involved physical exertion?
A game to me is based on luck but a sport is down to skill, so yes, I think it is a sport. Glad to see it included in the Olympics. Darts is played in pubs so people think of it as a game, but snooker is played in pubs and clubs and that is thought to be a sport!
I know there is a certain amount of skill required in card games but a lot of it is luck. If you don't get dealt the cards there's nothing you can do. I know, I've lost enough money at poker!