"I'm not talking about the graphic , i'm talking about the gameplay , balance , strategy."
It's fine to talk about gameplay, balance, and strategy, but graphics cannot be entirely neglected either. I guess ultimately it boils down to personal preference.
I view the differences between Broodwar and Starcraft 2 as points in favor of SC2, whereas other people in this thread look at the same points and score them for Broodwar.
To me, SC2 is the better game for the following reasons:
1. Every season there are a limited number of maps that are played on the ladder, which makes it interesting. When I stopped playing BW, there were 200+ official maps, but most games were either BGH or Lost Temple. I prefer the rotation of maps, while still keeping the pool down to less than 10, so that one can learn the intricacies of the maps and get variety as well.
2. The single player campaign of Wings of Liberty was the best Starcraft story in my opinion. It made a lot more sense than being forced to assist Kerrigan in BW, even though it was already clear that she'd backstab everyone. I also didn't want to support Alarac in the equally absurd Legacy of the Void Storyline, but again didn't get a choice. In Wings of Liberty at least there were some decisions to be made. Thus my personal ranking of the single player experience is as such: WoL, SC1, HotS, LotV, BW.
3. Multiplayer: Granted, the difference in skill was a lot more pronounced in BW. I remember a game where a guy rofl stomped me and my ally, because he kited Zealots with his Vultures, while also building up his base. With all the automatisms in SC2 the game is easier, but at the same time the matchmaking system with the leagues is a lot better than the old BW system. It feels good to work up from Bronze League to Platinum against players of comparable skill and there are still higher tiers that the competitive people can shoot for, while not turning off the bronze leaguers from the game. The hardcore audience may dislike it, but anything that brings in new players and keeps them happy is great, imho.
Those are my reasons and of course it is perfectly fine for other people to prefer BW for their reasons and the value they assign to certain aspects.