Ok, I admit Warcraft 3 has a pretty mediocre plot/story (I liked the characters a lot though, wich I consider part of the story). I didn't like Starcraft: Broodwar's story at all, due to the characters periodicly having the idiot ball slipped into their pockets just so Kerrigan can win. (The intro is just seriously amazing, though).
The original starcraft however, simply had an awesome story. I ordered and played it for the first time 3½ years ago, so there's no nostalgia filter regarding this one (and Brood War). the plot itself was extremely simple, but there's more to the story than just the plot. The dialogue was good, as were the characters. But most of all the way the story was told was great; It really felt like I was the main character, more so than with games with just a silent protagnist. That an ugly pixelated world could immerse me in it so was a real feat. I felt like a part of it and I felt a connection wih the characters (wich were nothing more than disembodied pixelated heads) because of how they talk to you. I could make a huge post explaining, but I won't, I'll just say I really felt a connection with these characters. The way Blizzard put the player in the story was just a great way of storytelling. Being a cerebrate in the zerg campaign, while the overmind gives awesome speeches, is one of my favorite gaming moments. Mind you, the gameplay of the campaign was absolutely boring, but the way the story was told and the characters were so engaging I gladly kept playing.
I can compare it to dragon age: very simple plot, but great story(telling). Starcraft2's story was just a complete joke, there barely was a story, characters were flat, downright moronic and their motivations unbelievable. There's no sence of urgency or sence of giving a crap about the game worlds. The lore was raped (retcon galore: a prophecy and the overmind was apparently a good guy all along) and the voice acting of Zeratul was just a joke. It was like an uninspired blockbuster movie. Story was thrown out the window to appeal to the lowest common denominator. It's not just story that was ruined. The multiplayer was ruined too, no LAN, the game was dumbed down, simplified and balanced poorly as to not be difficult for new players to play (for example, they balanced it around low-level play and 2v2 as much as high-level play), wich made pro games boring snoozefests to watch, ruining it as an e-sport for me too.