Many, Like D&D module B2, are simply a map and a list of what's in each room of the map. No cohesive plot, no unifying theme, just a bunch of prepared encounters that people can hang a story onto.
Still, the big difference between Keep on the Borderlands and GDW adventures like Annic Nova is that the D&D scenario provides players with something to fight.
The first GDW adventure I had ever seen was Shadows. I said to myself (being used to D&D adventures at the time, even ones like B2), "Kinda thin on what the PCs will fight." Then, I went out and bought my second Traveller adventure, Research Station Gamma, and as I looked at it, I said again to myself, "C'mon! Where's all the stuff to fight?"
So, I understand the sentiment in the OP.
When RPGs first began, it was much more common for a GM to create a sandbox universe for his game for his players to explore. Slowly, the D&D adventures started evolving, hitting the market--first like B2 but gradually growing into fully scripted tales with detailed plots--so that all a GM had to do was pick the adventure off the shelf, memorize it, and get on with the gaming.
I think there's merit to both styles of adventure. There is nothing like experiencing a game by a creative GM who toils and creates his own universe. It's an amazing gaming experience.
Then, again, buying a complete D&D-like adventure, off the shelf, can also be quite fun as it is like a GM with a writing staff to help him create ideas.
I tend to use both types in my games.
It's actually quite refreshing in a way.
Yes, much of Classic Traveller is designed for this type of play (and so is T5!). If you need TL 8 Marines for a country on a balkanized world, then change a skill or two (and maybe the enlistment throw) on the standard Marine career, and create as many as you need.
If you need robots in a scene you are planning, use Book 8 to create what you need.
If you need a special, non-standard sniper rifle, then adjust the DMs (including the scope) using the standard rifle as a base.
If you just bought Annic Nova and decide that some beastie from a world broke out of its cage and slaughtered the crew (experimental ship with experimental mutated animal cargo), then use the Animal creation rules to create an appropriate beastie and have a blast while your players explore the death ship that they've found in space.
Imagine the horror on some faces if this kind of thing was released now for any number of contemporary games (Pathfinder, D&Dnext, Eclipse Phase etc etc). GMs wouldn't know what to do.
They still do release this type of "adventure" for some games. Rare, but it happens. But, for most, instead of being labled as an "adventure", the term "supplement" is used. Same thing. It's a game aid to create a scenario for a GM's players. Different label.
Sitting here thinking about it, it feeds into the general feel I get from Traveller: "if you can make/build it work, you can keep/fly it".
Classic Traveller gives you all the tools you need to create your own interesting, involved universe.
I can tell you that there's nothing like creating this stuff. Most times, the enjoyment I get toiling around in my universe is reward enough for doing it. But, the icing on the cake is when your players take, during the roleplaying, what you've invented and then take it to a whole new level that you never expected.
THAT is one of the reasons I keep gaming, after all of these years.
