The gold edition is a highly recommended for RTS fans. The game graphics and animation is stunning, being able to zoom in full detail (with a computer with enough 3D graphics power) makes viewing the replay very entertaining.
The Winter War expansion includes the Imperial Guard, who are weak in ground troops (max squad size reduced from 15 in the original game down to 10. Their strength is in vehicles, more notably the artillery Ballisk and Russ tanks. Heavy infantry Ogryns gives them staying power, but are only available as their "tech" level develops.
Another downside is that the new programming reduces the strength and staying power of the Space Marines too. Their health upgrades only occur once they advance get to Level 1, no longer do they have the health upgrades at Level 0 and 1. This makes a big difference in multiplayer mode where Orks can simply rush and hack their way to victory, it is very hard to kill Orks in close combat with basic level units. It becomes very difficult to defeat the computer in Hard mode as they get their leader unit at the start. Trying to kill a leader unit with basic infantry units for any race is impossible. The only way to counter a quick rush is to quickly build listening posts and weapons platforms for defense against their avenue of attack.
The Winter War expansion campaign consists of 5 Order and 5 Disorder missions. The last two missions for each side can be played as one of four races, Human or Eldar for the Order, Chaos or Ork for the Disorder. Each mission for each race occurs on the same battlefield map, but each has separate mission objectives. Basically the player gets to fight each battle from each different side, pretty neat playability concept.
The fourth mission is perhaps the toughest one to complete as the player is not only competing against the other side, but also the other "ally". They key to finishing the 4th scenario is to pick one side to play and stick with it. It is not designed to have the player play both "allies" and win, only on side can win the mission.
The fifth and final mission pits the victor fighting one final battle against not only their arch enemy, but also the Necrons. Each race has to perform special tasks to win and defeat the Necrons. For the Imperial Guard, the key is to fortify and develop defense in depth before attempting to rebuild the Titan, landmines really slow down the Necrons. The player will also need a couple of Russ tanks and four artillery Ballisks to defeat the Necrons. The other races don't have the luxury of time and will have to balance developing their defenses and accomplishing the special tasks.
This game is very enjoyable if one want to simply play by building units and fighting battles. This is not a resource gathering game like Rise of Nations or Empire Earth. The player is often capped at three "builder" units, which fits the game really well, there are only two resources to collect (requisition points by capturing strategic locations and energy by building generators). Once a resource collection structure is built, it automatically generates so the player isn't distracted in having to assign more "workers" to harvest resources like in other real time strategy games.
Each race also gets a "super unit" if they are able to capture an artifact location. For the Orks (who are really fun to play) it is the Squiggoth, for the Imperials it is the Baneblade super tank, the Eldar and Chaos get their super warrior / demon while the Space Marines get the Rhino tank/ transported (personally prefer the Predator tank myself).
The game has relatively small armies and limited battlefields. The game is typically capped out to approximately 6-10 squads and 5-8 vehicles per race. The battlefields are well balanced, each starting area is given the exact same strategic locations and are a mirror image of each other. However, there are only a few main attack avenues and with the small number of units, it makes developing two attack groups and one defense group hard to perform. Once a player is able to advance and secure an opponent's strategic location, their forces are reduced and will need time to reinforce before continuing to advance, by then the opponent may have already recovered and will be ready to slug it out again. Had there been bigger battlefields and larger armies available, a player could continue to attack and exploit success with a follow-on attack, like in Starcraft of Age of Empires 2 (both can have max population of 200 with very large playing areas).
Bottom line, one of my friends described it the best, W40K Dawn of War is like playing paintball-speedball/ laser tag, quick and balanced playing fields. Age of Empires 2 is like playing a paintball game in a field, larger area to cover, more players, not always balanced terrain, and takes more time to finish. All are fun to play.