Do people that complain about having 1 campaign even know anything about it? Doing all 29 missions on brutal isn't a quick or easy feat, and there's fairly amusing tidbits after each mission that makes the whole thing more enjoyable. Customizations, plot choices, multiple side plots, and achivements also adds to the experience. It isn't just a plain, straight forward cycle of dialogues and missions. To me it was a really surprisingly immersive campaign.
The game isn't even just about the campaign. The multiplayer experience is what you'll be doing after you're done with the single, assuming you start with the single. I've played a little over 300 games of mp, and they're all with friends and we have fun. You can log on, easily see if you have any friends on, and be playing a match within 2 minutes. Additional features such as record tracking, match replays, looking at your friends rankings, and potraits rewards makes it all worth it. I can see who of my friends suck, watch replays of why I suck, and half of the time play against people who suck more then I do, thanks to the (odd?) matchmaking system.
You might not care for a particular feature, but there's something for everyone. Single players. Casual players. Hardcore players. Achievement whores. Challenge seekers. I wasn't going to buy it in the first place, but most of my friends were and I wanted to play with them, and it turned out well.
Now, seeing how the core engine and bnet is already there, paying $60 for the other 2 games might be a bit much. I'd say $40, but maybe Blizzard will suprise me again.
PS "Activision Blizzard, Inc., formerly Activision, Inc. (NASDAQ: ATVI) is the American holding company for Activision and Blizzard Entertainment, majority owned by French conglomerate Vivendi SA." Activision doesn't own Blizzard.