CT is a neat game, that in 1977 was way ahead of it's time. Today, it probably looks kinda funky in some ways, and very conventional in others. It still has some features that set it apart from all other games. These are the things that make Traveller really unique, and creates that "Traveller" feel.
A brief outline of CT in a nutshell...
- Skill Based task resolution. All dice are d6. 2d6 skill rolls, higher is better, skills generally add to the roll, or in opposed checks reduces the opponent's roll. Damage rolls can include more than 2 dice.
- Characters are defined primarily by characteristic scores and skill ratings. No hit dice, hit points, or any other ratings except psionics.
- Characteristics are on a hexadecimal scale (0 - 15) and include Stength, Dexterity, Endurance, Intelligence, Education, and Social Standing.
- Chargen uses a mechanic called Prior Service. This is the heart of CT. Instead of a point-buy system, characters are randomly generated. In fact, character generation is a mini-game within the game. It's simple and fast - you may generate multiple character profiles before settling on one you like.
- Prior Service not only determines your starting skills, but can also grant characteristic boosts, starting gear (up to and including the use of a small starship), special awards or social benefits, and cash. Creative use of Prior Service can create a ready-made character history.
- Prior Service gave CT a very modern feel because it assumes most "adventurers" are past members of certain careers. The initial core rules focused mainly on military careers (Navy, Marines, Army, Scouts, Merchant, or Other). There is no other distinguishing feature that sets adventurers apart from "regular folks".
- A basic military service model of character enlistment for four-year terms of service is used for all careers. Characters may engage in multiple terms of Prior Service, or none. Characters can also switch careers. Thus starting characters can vary greatly in age, skill, and benefits.
- Later supplements greatly expanded Prior Service both in depth and breadth. Terms of service became detailed character development chronologies, and expanded career choices included diverse examples like Pirates, Diplomats, Barbarians, Rogues, and Scientists.
- CT includes NO FORM of experience points. There is no model for further advancement in the basic CT rules - additional training was handled on an ad-hoc basis by the Referee. Gameplay in Traveller is not oriented around constant character stat/skill advancement.
- Combat in CT is a fairly simple abstracted rounds of movement and attack rolls. The combat round is roughly 15 seconds, although in Book 1 this is completely abstract (IIRC).
- Circumstance modifiers include a weapon vs. armor modifier matrix, similar to the old armor mod table in 1E AD&D. Later versions of Traveller evolved this into actual penetration rules, but CT is much simpler.
- Movement and attacks are both simultaneous, and handled seperately. Everyone declares movement, then everyone resolves attacks. There is no initiative in CT.
- Damage is rolled with multiple d6's. Wounding is modeled as temporary characteristic damage. Damage is applied to Strength, Dexterity, and Endurance, as the player chooses. However, each die rolled represents a distinct block of damage, so the characteristic reduced is chosen on a per die basis.
If some of that seemed kind of strange, remember that Traveller has a totally diferent vibe from D&D. Gameplay and character advancement are mainly oriented around social interaction, economic gain, and sheer narrative. In many ways, it is the Anti-Diablo, so to speak. (I love Diablo, btw - I'm strictly making a stylistic distinction here, hehe.) The two most popluar campaign themes in Traveller have been
Mercenaries - ex-military hired 'trouble-shooters', and
Free Trader - self-employed entrepreneurs with a starship mortgage and a narrow margin.
Additionally, in its purest form, CT was about giving design and modeling rules in a generic, abstract form. So setting elements like vehicles, starships, and whole worlds can be designed on paper using standarized rules. This is a major element of the Traveller tradition. Later supplements, editions, and spin-off games include some very, very crunchy bits indeed. An example of this is the old Trillion Credit Squadron tournament. This was a tourney format for conventions back in the 80's where each player designed his or her own fleet of starships around a set budget of 1,000,000,000 credits. You then compete with your fleet in a wargame with the other players to determine the winner.
Right - I'll stop waxing nostalgic here. Hopefully, this overview was helpful...
