Just to pipe in here, I'm a longtime 2300 lover, perhaps the only one who still plays 2300 using 2300 rules on this board...but I'm not going to sound like it. Why? Everyone else has sung to you about the good parts of 2300. As a longtime player of 2300, I feel obligated to point out the flaws of the system. There's lots of 'em, unfortunately. Fortunately, they're not unpatchable, but you should aware of them before you start playing.
2300 is the ultimate "style over substance" game, the feel of the game is probably the best of all of GDW's products (save perhaps T2k if you were playing it back before the breakup of the Soviet Union). However, the mechanics are actually cack in many ways.
If you're a longtime military RPG player you're going to be thrown off by a few things:
* 30 second combat rounds. 30 seconds is just too long of a time slice for a "modern" mobile firefight. (I would suggest reducing the rounds to 10 or 15 seconds and tinker with movement rates accordingly - the RoF of guns will go up, but not so much that anyone will complain so don't change those.)
* It's really, really, really to hit with a gun. Like ludicrously easy to hit. (It makes sense under the 30 second combat turn, but it's still excessively easy to hit IMO. I introduced an admittedly clunky +2 modifier for all tasks performed in the rush of combat, including shooting.)
* Weapon ranges are screwy - everything just has too long of a range. This long range, combined with the double DPV rule is pretty fun for letting small arms penetrate through thick armor, but given the ranges that most roleplaying game firefights occur at ( > 20m usually, with long range being 100m), you as might as well just double the DPV of everything. (Personally I chop gun ranges down a lot and make double DPV good only for very short ranges (~ 5m or so). At all other ranges, rolling a natural "10" or hitting a Formidible task lets you double your DPV - this represents the bullet getting a good angle or just penetrating through a joint in the armor or something.)
* Movement and throw distances are totally screwy, especially the throw distance - simply put, everyone in 2300 is a genetically engineered ubermensch. (Encumberance is pretty loony too. They're all holdovers from T2k that I don't think GDW ever really resolved. I'd go with STR x 2 for throw range with reasonable accuracy of a 1kg object)
* Tell your GM (if s/he's never run 2300 before) to be really wary of careers introduced in supplemental material. If you thought the careers in the basic book are poorly balanced, the ones in the supplemental material can be out and out loony in power inflation (don't believe me? Find the Aurore sourcebook and look at the skill package for the Bounty Hunter. Now compare him to Ground Military or Troubleshooter).
* As some of the posters here have mentioned, combat tends to be really deterministic, but because of that, it's very fast. You'll always know if your weapons can hurt someone even before firing your first slug most of the time. GDW never really overcame a recurring problem in their games - bullets either bounce off of you and you laugh at them or it gets through your armor and makes you explode into a fine red mist. There's no in-between. While this can be argued as realistic, it's not very fun. (Rolling for double DPV will get rid of this some as players won't be able to blithely declare "those are FAM-90s and they have no grenades, I just walk into the middle of the room and melee the enemy to death.")
* Missiles are vicious. Most vehicles don't have a chance against these harbingers of the end days, especially any vehicles that players are likely to have. (For missiles, I've introduced countermeasure devices and bring in pilot/driver skill to modify the homing roll. Yeah, it's cinematic, but having some Stimpfe with an Ohu blow up your vehicle with a EP25 missile and wiping out the entire party because they can't miss just isn't fun for me. Another good one is just to avoid letting NPCs or players have missiles.)
* Autofire rules are disgustingly effective at the very short ranges that roleplaying game firefights usually occur at ( > 20m). Eventually someone is going to figure out that ammo is so cheap that you don't actually need gun skills. Just empty your clip into your targets and let the mechanics of autofire take care of everything.
* 2300 and Star Cruiser's Space Combat System has a single, fatal flaw: Some starships can outrun missiles. This single flaw doomed Star Cruiser. If you have missiles and they have missiles and you can outrun enemy missiles and they can't outrun yours, you win. That's the only rule you need to know. The Kafers are doomed in 2300 because of this. Kafer missiles and ships move slowly and they can't shoot many of them at a time (oddly the Kafers are a bigger threat in 2300 basic space combat system because the X-Ray missile has an impressive speed of 14 which is reduced to a piddly 6 or 7 in Star Cruiser). Top of the line human ships can outrun Kafer missiles and fly circles around Kafer ships. There's no good reason why a Kennedy class cruiser should ever get destroyed or a Suffren for that matter. Besides being used to shoot down enemy missiles, the laser mounts on ships are pretty much just there because they're impressive looking.
Originally posted by Michael Brinkhues:
+ The Colonial Atlas is a MUST for the game IMHO
+ I'd add that the Aurore Sourcebook is just as critical for 2300 as the Atlas as it really gives you the nitty-gritty of what it means to live on an alien planet. The alien biosphere is great stuff (though everytime we go into the mushroom forests, some comedian at the table has to start making Warcraft II Orc jokes) and will really give the players the feel of living on an alien planet.
+ Nyotekundu isn't as useful as I thought it'd be, though if you like to play a more "Event Horizon" kind of game, get Nyotekundu (just be sure not to kill Lady Sandra Cathcart - she'll be important later on where she can keep the players from getting killed in the Avenger during the Invasion).
