Spaceflight simulators have been around in many forms for over 15 years now, and for the most part they generally take on one distinct form or another.  Some games are linear and have the player complete missions in order to advance the story, and others are privateer sims where the player has freedom and the object of amassing wealth and a powerful space ship. Battlecruiser Millennium, on the other hand, allows you to do so much more than your average space sim.  If you've ever dreamed of commanding a capital ship complete with its own crew, then BCM is your game.  Commanding ships aren't the only thing you can do; you can instead choose to play as a fighter pilot or marine. 

As commander, you are given your own capital ship, either a carrier, transport, or cruiser (ship classes are dependent by race and caste) and are responsible for the ship and its crew.  Based on your caste (military, explorer, paramedic, commercial, trader, etc), you'll have different things to do to serve your people and government, and you'll see more or less action based on your initial choices.  You can take your ship anywhere in the galaxy via jumppoints and wormholes, though you won't always meet friendly faces.  You are not limited to the coldness of space; you may enter the atmosphere of planets and moons and land on their surfaces as well.  Many planets and moons in Sol (including the moon), as well as in other systems can be visited, and they all have their own unique climates and topography (just don't attempt a water landing...).  Some planets and moons are empty, while others have cities and bases on their surfaces.

Commanding a starship is the most complex aspect of the game.  Your bridge crew help control ship operations, and your personnel work to keep the ship and its crew in good shape.  Medics help your crew recover from injuries, while engineers repair, replace, and upgrade vital ship components.  Marines are used to defend your ship against boarding parties and to prevent prisoners from escaping, or they could be sent to attack enemy bases on planet surfaces or capture space stations.  As a commander, you are not limited to the bridge of your ship; you could choose to pilot a shuttle, fighter, or ATV (typically used by marines on planet surfaces).  If you want, you could even walk around on the outside of your ship or fight on a planet's surface.

Your starship has many important facilities and systems on board that can be damaged in the course of a battle or in hostile environments.  If your medbay is damaged, wounded personnel may not be able to recover as quickly.  If turbolifts are disabled, your crews may not be able to get from place to place quickly.  Some facilities and systems are more important, such as life support or nuclear reactors, while others can wait until later, like research labs.  Your starship also requires fuel to power its systems; radine is needed for nuclear reactors, plutonium for shields, and irridium for cloaking devices. 

When you command a carrier, you have fighters that can fly in space and in atmosphere, and are used to protect your carrier as well as seek out enemy targets.  Carriers are slower and have less firepower than cruisers, but they make up for it with the increased marine capacity, a cloaking system, and the presence of fighters.  Both cruisers and carriers can carry shuttles, which, though unarmed, are good for evacuating personnel, deploying mining drones to collect minerals, rescuing other units, and towing ships.

If you choose to play as a fighter pilot or a marine, the game is much less complex.  Both may be deployed from carriers, space stations, or planet bases and engage threats to their assigned base or conduct strike missions against enemy targets, depending on what type of pilot or marine you are.  All marines are assigned jetpacks.

BCM is best played in a roaming campaign which permits you the ability to travel the universe and do what you want. BCM also features a number of scenarios to help you practice playing in different situations, and a full campaign (though the missions are incredibly difficult, even for seasoned veterans of the game).

The only real problem with BCM is the incredibly steep learning curve.  The best way to learn BCM is by playing as a cruiser or carrier commander because it offers you the ability to try everything the game has to offer.  A copy of the manual is also important.  Another problem, albeit a minor one, is that certain castes don't play very well in BCM, such as science, police, or explorer.  Everything in BCM is in real-time, so you may have to let your ship land on some uninhabited moon somewhere while your mining drones harvest minerals or your crews rest; nothing will happen while the game is not running, so you'll have to keep it active during that time.  BCM does not take to being minimized very well, so you'll have to use another computer to do things if you want your ship to continue operating.

BCM was made a freeware game to advertise the future projects the creator has in store.  The Universal Combat games are MMORPGs that allow you to play with other people; there are a number of fleets led by individuals who determine the duties of members.  Unfortunately, the Universal Combat games are not yet freeware.