I'm an amateur writer, linearter and interested in learning to mod for Command & Conquer Generals and Star Wars; Empire at War.
Extremely fun game in both campaigns and the skirmish mode. The sheer number of mods available, plus the ease with which they can be installed is just another plus in its favour. I'd rather play this than most modern strategy games.
Ah, where do I start? One of the most demanding games in the Real Time Tactics genre. The constant strain of making the most of your limited supply of munitions in missions where resupply was impossible and units had only what ammunition they brought with them, to the constant shuttling of supplies to other units holding off enemy assaults.
In many ways I think this was the grandfather of the Wargame series. Dozens of units arranged on the battlefield, the careful coordination of infantry, support weapons, AFV's and even limited air support, the sheer variety in the units you can get.
The campaign feature where ranking up by completing missions and thus unlocking more advanced units was much appreciated as well! Overall...it's a classic. Just go and try it, I'm sure there's a demo lurking about on the internet, and you can pick up the game and both its expansions (Fall of the Reich, focusing on the late-war Eastern Front, and Liberation, focusing on the Italian Front) for £4 on GOG now. That's a bargain.