The skirmish modes, whether space or land battles, play a little differently than they do in the campaign. Campaigns and galactic battles do all research and unit construction in the galactic map, the only construction done on battle maps during a campaign is automatically by space stations, or the building of turrets and support structures.
In skirmish battles, the game plays out very similarly to a regular RTS. You have a 2D movement plane, interrupted by features like asteroids or ground terrain deformations, and there are resource collection points that must be built on. These are limitless but do have a fairly moderate resource extraction rate. The resource, specifically ore, is converted into credits automatically and there are no alternate materials to worry about. Units are not built by buildings specifically, but hyperspace in or are dropped off by space shuttles. In land battles, the key is to control landing sites, which permit forward placement of units. In space battles, there is really no such restriction.
Most units have one or two special abilities. Sometimes, these are fairly basic boosting attack power at the cost of shields and speed, or taking cover to take less damage. Some units have abilities that have more specific and unique uses, such as the Interdictor cruiser, which is an Imperial unit capable of preventing enemy ships from hyperspacing out of a battle in campaign mode, or interrupting the target lock of their missiles.
Then, of course, there are the hero units. Darth Vader, Obi Wan, Mon Mothma, Emperor Palpatine, Boba Fett and others are available in land or space battles some, like Boba or Vader, can be useful in both. They typically have very powerful special abilities; Vader is capable of taking out a fair-sized Rebel ground force by himself, while Han and Chewie in the Millenium Falcon will make mincemeat of anything in a space battle under the size of a frigate. The game has balance problems when played seriously, and the hero units contribute greatly to them.
Then again, Empire at War is definitely not meant for serious play, never mind competitive. It is a fairly light game, highly entertaining at what it does ie, providing a decent all-around Star Wars strategy game but it is not deep. Hardcore RTS players are liable to be disappointed. Strategy gamers in general are also likely to want more complex features like RPG stats for their units or a morale system. This, we feel, would ruin the elegant simplicity of Empire at War. The most depth that can be found is in controlling key planets on the galactic map, planets that give various bonuses, and those that permit the construction of the best ships like Star Destroyers and MC80 Cruisers.
We experienced highly frustration problems in connecting and playing multiplayer matches at launch, but two quick, successive patches fixed things right up. Moreover, we applaud LucasArts for investing in a patch download system that is fast, efficient, and painless. No longer do you have to muck about fifteen different download sites, queuing up just to get pathetic 20KB/s download speeds. Its about time a publisher took responsibility for its own QA problems and provided an easy patch process for PC users. This is not a LucasArts innovation, but other than Steam, so few other examples exist that we have to give LucasArts credit for their effort.
Ultimately, however, the multiplayer is what suffers most from the lack of depth. The multiplayer skirmish battles are particularly affected, while the galactic conquest campaigns with Rebels and Alliance facing off against each other across 40 or so planets offer a better value. Just be sure that you and your opponent have the same idea about whether or not you want to fight the tactical battles.