Even though I only have 2.3 hrs on record in Steam. I bought this game on the disk (yes disk) around 10-11 years ago when it came out.
The online scene was buzzing and me and up to 6 friends used to constantly skirmish on Gamespy Arcade. Now Gamespy is dead, you can only play another player through the IP option which is a little fiddly, but it is doable.
The AI in this game is pretty good and you dont need to play humans to be challenged. The game is a timeless gem and I would recomend it to anyone. Crusader is by far the best in the series. Stronghold 1 is great is your playing the campaign. But I wouldn't go any further down the line than that, Firefly studios went down hill.
If your in to top down stratergy games, this game is amazing. I'd advise you watch Total Biscuits video on it, he explains it very well.
Go buy it, then contact me on steam if you want a game or a co-op partner! :D