Exploding sheep! (see below on details, details, details)
Just about everything.
To start with, it looks great. There was some 3D rendering done that makes the top-down view look better than games 3 and 4 years older than it (like Age of Empires II). Other graphical enhancements make the game flow very smoothly.
There's always background music - which was picked perfectly - and sound effects are classic. You will laugh out-loud the first time you hear "They're destroying our city!" until you realize your city is in deep $#!^.
The story line is on-par with great RPGs - something often overlooked in many RTS games to begin with.
You get to play both Orcs and Humans, and while each has similar units, they're different enough. Example: Orcs have peons, Humans have peasants. Both pretty much do the same things, but peons *sound* like peons, and peasants *sound* like peasants. Each has their own individual sayings. Same for grunts/knights, trolls/archers, all the way up to death knights/mages. Extreme thought went into making it balanced AND different. Death knights can raise dead (when bodies are around) and cast destruction spells (death and decay, anyone?), mages can cast invisibility and fireballs. Paladins can turn undead (which hurts and scares death knights) and heal. Ogre mages can cast floating eye-balls.
Details, details, details. While waiting for your peons to collect gold, you start clicking on them over and over again, and you find out that they start to get pissed off at you! Turns out *every* character in the game will get pissed off at you, and each category of character gets pissed in different ways ("Don't you have a Kingdom to rule?")
Map editor to share with your friends.
One CD can play four people at the same time, up to eight can play one game! Full-fledged ability to play any of the multi-player maps - no cheap spawn copies that only let you play a little bit.
On my 1.2 Ghz, I can't figure out how to slow down the mouse scrolling (I've tried the options menu, it doesn't work).
Some of the battles got a little long, some were more difficult than I cared for (I *LIKE* taking in an army of Death Knights...what do you mean that's all the gold I get?!?)
The Bottom Line
Don't let the Real-Time Strategy portion get you down. It may be that, but it's so much more. It's just a fully-enjoyable game that will keep you laughing and playing for a long time. Even my wife knows what happens after I say "My tummy feels funny... ."
Blizzard was so financially set after this game, they could have just created WC3, 4, and 5 all based on the same basic game and retired. They didn't. I can only imagine that they didn't want to detract from the game in some way by screwing it up with cheap or cheesey add-ons or sequels. There was only one real add-on, and there were similar games like StarCraft, but even that was quite different.