First acknowledging the other posts with valid criticisms, I want to pile onto David's:
So, to pile on:
The ship design system, created for player starships, has a better scope than previous editions, without being as complex as MegaTraveller design. It ties up loose ends with 'canon', and consolidates where useful. For example, we now know the probable tech level of the ANNIC NOVA, and how to design it. Small hulls are usable for small craft, cargo pods, and drop tanks. Drives may resemble Book 2, but it works more like High Guard, backed by formulas. (And yes, there is errata)
Character creation got a great shot in the arm by supporting aliens. One major drawback in creating new aliens ("sophonts") was that you had to create career generation tables, new skills, and new characteristics, plus the rules for using them all. No longer. Alien modules just got a dozen pages skinnier. Another feature is that robots, if capable, can go through the career process. This streamlines all non-human player characters into the game. And there's a method for randomly generating new aliens -- which also doubles as a guideline for crafting your own.
Finally, I feel that Traveller needed a gun-design subsystem that doesn't make my head spin since 1980. And I think Traveller5 is that system. And the armor design subsystem is the same kind of thing.
What does T5 fix? Well if you felt the physics based design systems like FF&S were too complex T5's description based design systems are simpler if a bit less flexible. Even starship creation is mainly CT book 2 with lots of bells and whistles added.
[...]
Character creation is great, the best it's ever been. As detailed as CT/MT advanced character creation but almost as fast as CT basic character creation once you know what and where everything is.
The introduction of standardized rules for sophants, chimeras, and androids were long needed and are much appreciated.
With all of the design subsystems in the core, T5 has the potential to be truly internally compatible from the start and avoid the kinds of ugly, tacked-on subsystem messes that occur when things like armor and weapon design aren't used to design the weapons and armor in the core book.
So, to pile on:
The ship design system, created for player starships, has a better scope than previous editions, without being as complex as MegaTraveller design. It ties up loose ends with 'canon', and consolidates where useful. For example, we now know the probable tech level of the ANNIC NOVA, and how to design it. Small hulls are usable for small craft, cargo pods, and drop tanks. Drives may resemble Book 2, but it works more like High Guard, backed by formulas. (And yes, there is errata)
Character creation got a great shot in the arm by supporting aliens. One major drawback in creating new aliens ("sophonts") was that you had to create career generation tables, new skills, and new characteristics, plus the rules for using them all. No longer. Alien modules just got a dozen pages skinnier. Another feature is that robots, if capable, can go through the career process. This streamlines all non-human player characters into the game. And there's a method for randomly generating new aliens -- which also doubles as a guideline for crafting your own.
Finally, I feel that Traveller needed a gun-design subsystem that doesn't make my head spin since 1980. And I think Traveller5 is that system. And the armor design subsystem is the same kind of thing.