I think that Zerg are the most unique:
- They regenerate health over time;
- They use huge flying Overlords as a supply, transport and detection;
- Their buildings are basicly alive non building, but actually the mutated Drone;
- Unlike humans and protoss their strength is in numbers;
- Darwin was right! They evolve;
- They have a town hall in tiers, again they evolve;
- Their buildings regenerate just like all normal units;
- They can infest the terran base to make suicidal humans;
- They can go underground with burrow or underground channel;
- Their units are cheap, cheaper than terran`s or protoss`;
- They only have suicidal units one for ground and one for air;
- They build faster than any other race.
Maybe there is more because i can`t remember it all!
For me Zergs are the most unique.
Ah, talking about sc1 I see DEAD FiSH?
Well, in sc2, I would have to say that being a Zerg player originally, I got bored of it pretty quickly when it became apparant that certain builds are just designed to take out each race, thus making their gameplay seem somewhat less interesting. But that may be after large numbers of games being played as Zerg.
However, now playing Protoss, they offer a lot of unique gameplay ideas. But I would have to say that Terran is even more unique, as they are amazingly hard to play (I can't get into them personally), but while they're amazingly mobile, they have limited potential for speed without sacrificing their own health. The way a good Terran player makes up for this is quite unique imo. Also, you can expand in your own base and then lift off as desired. Among many other things.
Or else. But I think they will because zergs have already lost, Mengsk is next to fall in Zerg campaign (well Kerrigen is with Jim and its not really hard to guess who is next on jims target list) and then as the "epic" end it will be hybrids for protoss.