The Player Character Classes In General
The SG-1 roleplaying game has a total of six base classes in the core book, compared to the eleven core classes of D&D. There are reasons, however, for this small number. First of all, the classes in the Stargate game are fairly flexible and can be used to cover multiple concepts. While there are certain things that set the classes apart from one another, most of them have options in the way of feats and skills. Secondly, it's likely that new classes were slated to be released in upcoming supplement books. Thirdly, the main book gives DMs all that they need to create classes of their own. Perhaps more importantly, Stargate encourages multiclassing, and there's no experience penalty for having multiple classes at once. This makes the six core classes even more flexible. By using the options of one class, or by combining the right classes, one can cover a lot of character concepts.
Every class has one special core ability that is gained at first level. A character can only have the core ability of their first class, and can never have more than one. This shows their initial specialization and focus, and ensures that all characters get only one of these perks.
In addition to the normal things that go up per level, a Stargate character also has a gear picks rating and a resource points rating. Gear picks enable a character to pick extra items of gear to take on missions. The number of gear picks given by classes are also used to decide when a character goes up in rank. The gear picks rating goes up steadily as characters gain levels, but this rating is also added to the character's Charisma modifier to show how being likeable can get you extra perks (even in the military!). Characters are not supposed to share or trade gear picks. On the other hand, resource points are made for sharing. Resource points are pooled amongst team members to requisition special items (like alien technology) or services (like having an advanced team sent ahead to get a little information about a planet).
In this way the game links the best and greatest amount of gear to advanced characters, which is the way that most roleplaying games are set up. Other roleplaying games place a greater emphasis on money, however, and on the acquiring of personal gear that is then used in every circumstance. The Stargate game allows characters money but there's only so much that they can buy that is legal or available. Also, Stargate is a military game, and part of the military experience is having your gear requisitioned to you.
All of the classes in the Stargate game gain bonus feats of some sort, and most of them gain related feats (working their way up a specific feat tree). This game has a truly amazing selection of feats to choose from, and a great deal of them are useful and desirable (unlike a lot of other gaming products).
Character classes often gain skill bonuses or even ability bonuses in Stargate, as well. Most classes gain special abilities that go up as they advance in level (so that the explorer takes less and less time to do research as they advance in level, for example).
The Classes Themselves
When I first saw the Explorer class, I thought for sure Daniel Jackson would be listed with at least a few levels of Explorer later on (although he wasn't). It reminded me of Daniel, who is very smart but who has also learned to defend himself. On one hand, the Explorer is a class for people who travel the world and learn to deal with its dangers. It is not a heavy combat class but it does have some ruggedness to it, like Uncanny Dodge, and the opportunity to take bonus combat feats. On the other hand, the Explorer class also takes into account the knowledge that comes with exposure to other places and cultures (and instead of taking bonus combat feats, the explorer has the choice to take skill feats instead). This class is a good mix of bookishness and toughness.
The Guardian class is the typical class of the Jaffa. It is certainly a heavy combat class, with most of its special abilities geared toward a solid self-defense. A character has to be a Jaffa in order to qualify for the class, however.
The Pointman is a very interesting class; it appears to be designed for leadership. It has the best gear pick progression in the game, which it shares with the Scientist, but the Pointman gains more vitality points and more weapon and armor proficiencies. The Pointman also has the ability to boost the rolls of teammates in several different ways, making the entire team more effective. Last but not least, the Pointman is able to choose cross-class skills and some abilities.
The Scientist is probably the least combat-ready of the core classes but is also the most knowledge-capable. Nearly all of their abilities have to do with skills and Intelligence. While this may not seem particularly useful to some at first glance, one must keep in mind that Stargate is a science fiction game. The show itself has a lot more science than most groups are probably going to get into, but the Scientist's skills should come into play often enough. They get all of the computer and technology-related skills as class skills, not to mention the knowledges and languages. In a game with alien technology, races, and so on, a Scientist can end up being very valuable.
The Scout is a neat cross between a ranger and a rogue. They are able to track and to help keep a group alive, but they're also able to sneak around. They have a great potential for effectiveness in a travelling game like Stargate.
The Soldier is pretty much what it's called; like the Guardian class, it is a heavy-combat option. It has different abilities than the Guardian, however. Jack O'Neill is a great example of a soldier.
The Stargate game also has about seven NPC classes just for the use of the Dungeon Master; players are not allowed to use them. These are like the NPC classes found in the Dungeon Master's Guide but they are more suited to the Stargate milieu, replacing the magic of the adept with the knowledge of the academic. These classes are created to be weaker at every level than the normal player character classes, but to have some abilities to help or hurt the PCs.
There are two kinds of NPCs in Stargate: standard and special. Standard NPCs are the everyday Joes, the crowds, the armies, the villagers, the red shirts - what have you. They just aren't as skilled or well armed, and when a critical hit is landed on a standard NPC they are knocked out without further ado. Special NPCs, by comparison, are named villains or allies who stick around for a while. They don't have the restrictions of standard NPCs, but they can be made using NPC classes.