Well, we do play
our current Traveller campaign using a modified version of GURPS 3rd edition with some ideas taken from the 4th. I like the quick rules and we have kept the number crunching to a minimum with our modifications - as the GURPS system allows to either keep it simple or make it complex, just as the GM and his group wants it. It may have it's disadvantages but in general I think it is one of the systems I favour most as it does not tend to get in the way of our playing style. I do not like about 4th edition that everything has gotten more expensive CharacterPoint-wise without offering too much compensation - but that is just my opinion and depends on the style of play You are using as the old 3rd edition admittedly allowed more generalists that were better at what they are doing than the characters created with 4th ed. rules.
For starters with GURPS I advise getting the Basic 4th ed. rulebook and
GURPS: Interstellar Wars which nicely covers about everything You need to know about the Traveller background of the First Contact of us Earthlings with the Vilani Empire and the ensuing war. If You want to save some money get the 3rd edition rulebook(s) and GURPS Traveller (2nd ed): getting these books either as PDF or used should be rather affordeable and I actually prefer using 3rd edition rules. It is easy to adapt 3rd to 4th edition anyways.
@Rhialto: yes, most skills depend on either DEXterity or INTelligence, with a few exceptions based on STRength and HEAlth. With only four primary attributes that is nothing unusual IMHO: 4th ed. made the two primary attributes (DEX/INT) more expensive and few normal characters are able to raise these stats beyond the value of 13 without having to make compromises. Going below 10 in STR or HEA also lowers Your characters survivability as You have less hitpoints (which go on STR in the 4th edition, not on HEA anymore), less hand-to-hand damage and ability to use weapons with recoil or that require a minimum STR and less movement (total of HEAlth+DEXterity divided by four, rounded down). Movement also governs Your Dodge roll so You would not want to go down too far - and the mage needs the Fatigue points HEAlth provides for casting his spells, too. So both STR and HEA still have their importance - mayhaps less than before but this is covered by the different costs of the attributes.
Concerning books You "need" for a NON-Traveller SciFi campaign that uses GURPS Space 4th ed.:
Basic Rules and Space
Ultratech if You need more details about the technology for a campaign setting and You do not want to work that stuff out Yourself.
Hightech if You exspect campaigns to be around OUR current techlevel.
Spaceships if You want a really, really, really complex design system for starships.
Biotech if You want biomodifications to be part of Your campaign universe, perhaps Changing Times (the background for the Transhuman Space setting) might be the better idea.
GURPS Space as a standalone ressource for Traveller: hmmno, not really. Traveller is different and Space tries to cover every SciFi genre. You can use it but You do not have to.
If You want to be cost effective You can go for the 3rd edition stuff and use the
update rules.
