A game of vision, not adrenaline.
Most games are about excitement. I play games like Medal of Honor for the thrill of victory. Starcraft is fast-paced strategy excitement. Titan Quest offers fun abilities, while Mass Effect and other RPG games offer a compelling plot.
Rebellion offers almost no plot. Rebellion is not fast-paced. And while a well-placed headshot may give me a smug feeling of superiority or a thrill of quick victory over an opponent, Rebellion offers no similar quick endorphins. Instead, Rebellion gives you an open format and lets you decide.
We all know the Star Wars universe well. If all you know is the original trilogy, or even the first of those movies, you know enough to understand the back history of this game. If you have read the novels, played the games, and love every aspect of Star Wars, you will get even more out of this game.
Rebellion is set up for long-term strategical satisfaction. It actually takes time to build a kilometer-long starship. There are no super-units; balance is important. Research doesn't always work. In short, Rebellion is a mix of sci fi, video game, and reality.
Characters are recruited, then sent on missions. Intelligence is gathered slowly, and is not always reliable- sure, Darth Vader may have been on Corellia when Han Solo scouted the planet, but by the time Wedge Antilles arrives with a battle squadron, Vader has left.
Resources are gathered via mines and refineries. Maintenance of equipment is important- just because you can build it doesn't mean you can keep it running. This is the idea behind Rebellion: more realism.
This game provides players with the ability to do what they want. Make the Star Wars plot change, build a real fleet with the Rebel Alliance or use the Empire's starfighters to destroy the rebels. Train new Jedi, or new Sith. Assassinate enemy operatives. Bombard worlds into oblivion, or blow them away entirely with your own Death Star.
With great power comes great complexity. Most bad reviews are because of the time required to learn this game. If you don't mind actually thinking about your video games, you may ignore most of the bad reviews.
There is a learning curve. Once you have played the game for a bit, you'll find the AI is pathetically inadequate. Fleet battles are difficult to manage beyond the basic. Parts of the game are hardcoded and cannot be upgraded.
The Bottom Line
Graphics: Certainly not fantastic, but are acceptable except for fleet battles.
Music: Standard Star Wars. Neither spectacular nor bad.
Interface: Poor, but manageable.
Flexibility: Superb. Few games offer this level of options.
Final thoughts: a great game for thinkers. There is still a thriving community for this game: http://www.swrebellion.com/
The above website also offers tools like RebEd, which allows customization of units, build times, etc. Highly recommended, especially if you like the extended universe.