Growing up with this game, and playing it the most and extremely enjoying it, this is my favorite RTS of all time, and up there in my favorite games. It's pure fun. Now it's on Steam.
It's a little hard to get it going and working on Steam but just check out the Community Guides and install the Mod Complex. It isn't very hard once you pay attention to the directions and the games works perfectly plus some extras from mods of this game from the past. The only thing I couldn't get working was the in-game Steam overlay but I won't miss it that much.
The game doesn't require resources to collect or anything, just population and a troop max, which adds to the strategy because you have to predict what the enemy will show up with and use the troop max wisely to match their units and beat them. From my long, long, long experience with this game it relies on a big battle between two factions, and whoever comes out the winner with what troops they picked and how they used them, pretty much is able at that point to defeat that player... putting them in deep trouble. However, when you play with multiple CPUs, the AI will be smart enough to try and finish your army off if you lose too many troops and then you'll be the one in big trouble.
That's why I love this game: it's timing, your decisions, and pure military that control the battles.
The maps are pretty great. A lot of them are set up in linear terrain settings... which sounds awful, but Pyro designed these maps so well so that it isn't so straight foward. There's always another way to go, a different way to fight in *most* maps.
Graphics? This game is from 2003... you get what you expect. However, I say you get a bit more. Some people will probably disagree with me, but the game looks fantastic still! I think that this game has aged extremely well. Obviously textures have aged, but graphically, the heart of how this game looks and not the technical stuff, it's well crafted and meant to last.
Not many people play multiplayer any more, and even the Steam release hasn't breathed that much light into it. Through the game you can only use LAN/IP connections, but most people use GameRanger anyways. Not quite as active as say Rome: Total War, but there are some people.
There are a few decent mods for this game too, the best of which are included in the aforementioned Mod Complex.
The soundtrack is pretty fantastic and I wish the composer Mateo Pascual did more soundtracks. He's worked with Pyro Studios a few times, and done a few other things too, but this is certainly his pinacle. Seriously, I like this soundtrack so much I put it on my phone's music app (Google Play whatever you don't care haha). If you're looking for epic but intricate and catchy classical music with drums and symphonies, this is the bee's knee's.
This game isn't perfect though. Sometimes it's a bit reliant on "more men + better units = winner" type of strategy. It does take some time to figure out, but once you realize that this isn't how the game works, and you realize that nearly every time you fight someone you can beat them without following this strategy (or letting it happen to you), then this problem disappears. A lot of people feel that the troop max is annoying, but I feel that without it being at the limit it is, this game wouldn't be very difficult. Sure, I've said the AI is pretty good, and there are three different difficulties with a mostly decent difficulty curve, but the limit is surely essential, I feel. Gameplay wise, the vanilla game doesn't have an incredible amount to offer, but it's also $5 and like I said, it's very easy to install Mod Complex to get more gameplay-adding mods. The game can't nearly go to 1920x1080 resolution and has a lot more technical limitations than any modern game, but remember it's from 2003. Overall, once you get working, it's awesome. Buy it.