At the end of Brood War (I'm not putting spoiler tags), we were given the impression that the zerg had finally created Protoss hybrids. To me this mean they were going to take the current Toss technology, which was vastly superior to their technology, and meld with it creating a Zerg-Protoss hybrid race, with the original Zerg as their leaders, they could do a cool kind of hybrid rebellion where the Protoss Hybrids are pure evil.
The Xel Naga were HEAVILY hinted at appearing as well making them the replacement Protoss race and Terrans are humans, and will just be very intelligent from the previous war.
It is just an announcement, but this announcement has been anticipated since 2000 when Blizzard announced a new game was coming out, but we got Diablo 2. Again, when Warcraft 3 came out. We, the Starcraft faithful, were elated when we heard a HUGE announcement was coming, but we got World of Warcraft and we all saw that as Starcraft dying. This is the most anticipated announcement in the RTS community, if not the PC gaming community. So, yes, even just the announcement is a big deal.
Also, they better have StarEdit. That absorbed me.