Abruptly one day, as Earth was minding its own business, an alien race called the Chenjesu suddenly appeared in the Sol system and made some announcements: First, they themselves intended no harm to Earth. Second, there was a very powerful species called the Ur-Quan, which was bent on enslaving the galaxy. The Chenjesu and Ur-Quan were at war, and the Chenjesu requested the help of Earth.
Upon examination of the facts, Earth unpacked its long-stored nuclear reserve and allied with the Chenjesu. The ensuing war lasted for many years, and the humans were of very material assistance, but the eventual result was the victory of the Ur-Quan.
The principal vessel of the Star Control (i.e. the Terran command system) is the Cruiser. It is a slow missile platform with some weak auto-aim defenses. The MX missiles it fires are very long-ranged and tracking, but they do not track particularly tightly, so modestly fast ships can dodge with very high reliability. They pack a moderate punch, but cannot provide a fast kill against most ships. The missiles are also very fragile, exploding at the slightest touch (though they are strong enough to plow through Dreadnaughts' autonomous fighters, which must be REALLY fragile).
The Point Defense is supposed to be an actually-functioning version of Star Wars missile defense lasers. Ignoring the unwisdom of national missile defense, and the fact that a real system would not maintain a 100% accuracy rate like the Earthling Point Defense does, this system is great! It doesn't target only missiles, but also asteroids (its most useful feature) and the enemy ship. And when you activate it, it fires on everything it could hit, not only one! If there are many targets, the damage efficiency and rate of this weapon can rival that of the largest battleships in the game. Too bad it's so spread out though...
Why is targeting the asteroids the most useful feature? Typically, an Earthling captain finds himself flying backwards, firing missiles the moment he can at an enemy that is inexorably coming closer. At this point, the last thing you want to have happen is collide with an asteroid and find yourself coming into close range with whatever it was you are running from. With PD, you need not worry. Well, the Dreadnaught will probably catch up to you eventually anyway, but it won't be premature.
The cruiser is very strong against Arilou (ironic, isn't it?), Druuge, and Thraddash.
It has a slight advantage against Melnorme, Mycon, Pkunk, Spathi, and Ur-Quan (though it will almost certainly lose to the Dreadnought, it can inflict more than its value in damage). Against the VUX, it will win easily IF it can get some range. Against the AI in Star Control 2, an Earthling can easily destroy a Mycon, as it tends to use its energy to regenerate instead of firing.
The cruiser is somewhat weak against Chenjesu, Slylandro, and Umgah. It probably won't do its value in damage against the Kohr-Ah, if the Kohr-Ah fight defensively. It is not able enough to keep the Zoq-Fot-Pik at bay, and will thus probably fall to the stinger, against a competent pilot.
The cruiser is very weak against Androsynth, Chmmr, Mmrnmhrm, Utwig, and Yehat
This is not an exhaustive list, and of course good piloting makes most of the difference. I have assumed that the opponent is competent but not expert - some other races very much depend on the other guy, with not too much you can do about it.