One of the Greatest RTS games of all time!
The story begins a few years after the Humans beat back the Orcish Horde. The Alliance has been weakening with no action, so they are caught off-guard when a new enemy arrises, the Undead Scourge.
The main game is broken up into 4 diffrent campaigns, one for each faction. While the Human campaign is (at least to me) seemingly similar to Star Wars (a good guy becomes what he was trying to destroy), the missions are always engaging and fun. There is even a prolouge about the Orcs which teaches new players the basics and sets up the story.
The 2nd and 4th campaings are for the new factions: The Undead and the Night Elves. The Undead bear a great likeleness to the zurg from Starcraft, in which the faction dosen't have a lot of hardcore strong units, but prefer to swarm your ass with craploads fo units. The Night Elves (my new favorite race) are more of a magic using race that has dosent have buildings but more along the lines of trees that can move and attack and (during night only) can turn invisible. Bet thats a neat party trick.
Speaking of night, Warcraft is definitly a game that has realistic surroundings. There is a day-to-night cycle, which even realistically lowers your seing rate. There are animals that you can blow up (by clicking them rapidly), and nutral enemys known as "creeps" that you can kill for exp.
Another great factor is the Heros. Heros are, in basic, super units that can carry items and gain experience points for killing enemy's. Each faction has three, and picking which one to start with is the real challenge, because no two Heros are the same. Do you use the one that has awesome melee abilitys? To you take a support guy who can buff up your army? Or a magic guy who can harass your enemys base?
Speaking of Base, it is definitally a great part of the game, possibly the key part to victory. You start with a main base (Town Hall, Great Tree, Necropolis) and 5 workers. The Humans and Orcs have the same old Pesants and Peons and gathering stuff: You run to the mine to get gold and bring it back to the Main building, same with the lumber. The Undead and Elves are totally diffrent. Firstly, they have to either Haunt (Undead) of tangle (Elves) to gather gold, and then they don't have to leave the mine to gather gold. They just stand there and siphon the gold to the base. Cool. Even lumber gathering is diffrent: the Undead have to use their basic fighter unit (the Ghoul) to gather lumber, and the Wisp (basic Elves worker) latch on to the tree and collect the wood without damaging the tree.
Now that thats out of the way, we move on to building stuff, and even there the races differ massively. Peasents for Humans can team up on one building to make it faster, Undead can start a summoning and then leave the building alone while it makes itself, and a Wisp literally turns into a giant tree that can move and be used in base defense.
I could go on about the unit diffrences, but then I would probably make the browser explode, so I'll leave it at this: Warcrafts units are insanely diffrent, and there are multible strategys for each.
Now we go into the most important mode: Online, and it is awesome. Battle.net is totally free and easy to use, so finding a match isn't a problem. You can create a match, join an existiing one, or even just jump into a random match with players at your skill level. There are even clans you can join, and your record makes an impact on the clans rating. Now we know where Halo 2 gets it from.
All in all, Warcraft 3 is an insaney good game, and will give you tons of playtime, replay value, or even just finally beating that **** online that talks lots of smack but leaves when losing. Greatest RTS of all time? Hells yeah.