This expansion pack adds 15 new missions to the original Command & Conquer. As far as an expansion pack goes this one is pretty lacking; There's no new units and the missions don't integrate themselves into the main game at all (they're like side missions.) The missions themselves though are pretty challenging. Most involve some kind of objective to complete before you go all out and destroy the enemy base. They fit into the overall story line from the first game, perhaps as side battles elsewhere in the world. A few of them are pretty tough - even the best RTS people out there are not going to be able to breeze through them. For instance there is one where you have to evacuate these scientists from different points on a heavily guarded map with an extremely small force, all the while dodging squads of flame tanks that spell instant death for you civilian cargo, all under a strict time limit. Not easy in the slightest.
The missions here do not have any original FMV intros as in the main game, although some of the CGI sequences are reused here. Each mission starts with a short text briefing. Although there are no new units or buildings the missions here allow you access to units in a one player game that are normally only available in multiplayer, like chem troops and attack helicopters. However after installing this expansion pack certain units in the regular game will cost different prices for some reason.
In addition to the seven GDI and eight NOD missions there are also five secret "Dinosaur" missions, which are accessible by typing "C&Cfunpark" at the DOS prompt. The missions are pretty easy, send your troops out, kill the dinos. In the last one however you get to control the dinosaurs to destroy NOD which was pretty fun. Sad thing is there's only one mission like this. There is also a pretty large exploitable bug whereupon after quitting a dinosaur mission and starting a save from the regular game you get access to units higher up in the tech tree than what should be availible.
I can't really reccomend tracking down this expansion pack, only people who really like the original C&C are going to enjoy it. It really doesn't do enough to enhance the main game at all. However it's included in 2006's Command & Conquer: The First Decade bundleware pack so if you're a new player who bought that edition you have it already.