"Don't be too proud of this technological terror you've constructed." -Darth Vader
Good Against: Bombers, Heavy Bombers, Frigates, Carriers, Cruisers, Heavy Cruisers
Bad Against: Battleships, Dreadnoughts, Ion Bombers/Frigates
Why use them? They are very good at defending your mobile fleet while at the fortress. They aren't very popular due to very slow speed and they can't use Jumpgates, but the biggest reason is probably because they are so hard to get. They could be useful for attacking incoming cruiser/heavy cruiser fleets though.
Advanced tactics Death stars are very rarely used, and few people know how to use them effectively. Many people call them 'flying debris', and for good reason. Except in large numbers, death stars are highly vulnerable to many commonly used units in the game. They can be killed by ion units (or severely damaged), they can be shot by any unit above heavy cruisers and below themselves for good ratios, they are very expensive to repair, they are very slow and they can't use jumpgates.
So what advantages do they have? Well, for one, they give a 10% bonus in power and armour to your fleet, twice that of a leviathan. For this reason alone many players use them on their fortress base for defense. This isn't recommended for newer or "uncivilized" servers, because a death star on a base is practically an invitation for you to be attacked - the death star alone makes that attacker immediately assume profit can be made. Whether this is true or not is irrelevant, because that player will attack you due to the bad reputation that a death star has in the game.
Death stars are hard to kill in large numbers, but devoting effort into a death star stack means that your mobile will be useless in most situations. Only perhaps 1 player on each server has gone this route, but the results can be very intimidating. Since most players use cruiser/heavy cruiser fleets, perhaps 75% of all fleets can be torn apart by a death star stack. But the players that do have battleship stacks will absolutely destroy you if they do find you. Death star stacks can only effectively operate in one galaxy, so keep this in mind if you build one. It takes about 100 hours for a death star to move one galaxy, and about 1000 hours just to move one galaxy set. So they aren't going anywhere fast. Logistics commanders can help them move faster, however.
In the end, many players build one or two death stars just to say they have them, and then regret it ever after. One death star can be useful on a fortress, but only if it's backed by loads of stationary planetary defenses (rings and shields). For the bonus, a leviathan is probably more useful though.
- (x) in Shipyard indicates the number of Orbital Shipyards required.
- due to the tech level required to build them their stats are more Correctly Power:42075, Armor:31050, Shielding:114, and Speed 2. Thus giving them the ability to shield rape everything below battleships.