Not having to select research and wait for it to complete over a period of time
Well, science actually does take time when it comes to Research & Development in real life. Therefore, the player expects time shall pass between the beginning of a research and its final results, be it a couple of minutes or a whole day. At the same time, research isn't a linear process but it involves several steps: data gathering & analysis, experiments, testing... It usually depends on the field of study, e.g. robotics, biology, military. As a game designer, you can translate these aspects into opportunities to involve the player in the action; this leads to the next point,
Interactive and meaningful
How to bring the player into the research, making it somewhat interactive
Research, regardless of the scope (e.g. academic, industrial), needs resources: time, money, people. But also machinery, energy, materials, specimens, equipment... All these can become the first mean of interaction between players and your research system. Players can:
- Provide resources for a research job: by providing the bare minimum (for example: 1 scientist, 1 computer, and 1 additional item), the research can start and will take a given amount of time.
- Add more resources to a job: the player can increase the number of resources for a given job, e.g. putting more scientists to work or increasing/upgrading the current machinery in use. An upper bound is needed: an infinite workforce doesn't get the job done at a glance. Also, such resources aren't necessarily available to the player yet: if a research job is about a newly discovered mineral, more samples of such mineral are needed, and the player needs to go and harvest more.
- Parallel tasks: a research job may consist of different tasks that can be performed independently before joining everything and move to the next step (like collecting data before analysing it or testing a scenario multiple times). If this applies, you may let multiple groups research the same technology (not different ones, as you stated) so that the player gets multiple chances (alternate "drop system") to make major discoveries and unlock that technology level.
I'm thinking about how OS threads work: a single-thread task can be improved by converting the program into a multi-threaded application (although that's not always possible, depending on the task). Different threads could need the same resources, then race conditions may arise and are to be dealt with.
Consistent and progressive
A player should probably know at least vaguely what they're progressing towards, but maybe not all game content should be revealed to them
An individual technology's description should be fine to give the player a good idea of what they are going to get when unlocking that technology. You could include both a description ("Microelectronics - Develop fine-tuned devices and controllers to create advanced utility items.") and a practical summary ("UNLOCKS: Jump packs, Brain wiring, Compact weaponry... REQUIRES: 1 scientist, 3 silicon, 10 energy.") the player can read to get information at a glance. Additionally, the research tree can be explored only up to a certain depth level, for example, the next available technologies only, or their 1st-level subsequent items too.
On the other hand, implications of owning a given technology may be explicitly hidden to the player. They may not know how to combine two technologies works until they randomly find a blueprint/recipe of some sort; BUT they could also figure out themself, in which case the game provides the blueprints automatically for ease of access. If they manage to discover tech combos by themselves rather than waiting for blueprint drops (which are a useful way of preventing players to be stuck nonetheless) they will feel smart and clever and believe they are making progress. They will feel rewarded.
Research shouldn't be a chore, and every time a new technology is discovered/researched, it should be something to look forward to
Completing researches is something to look forward to if it is needed. Any technology knowledge must have a purpose, i.e. a direct (and useful) application in your game. Why jump packs? There are high-altitude areas not directly accessible. Ground-penetrating scanner? Because stuff may be buried deep down the terrain. Gunlink? Improves efficiency on the battlefield. Every technology in your research tree shouldn't be there only to unlock more: the player may decide to explore a different branch of technologies, therefore everything available until that moment should work without making them think something is missing. If every technology can be applied in the game rather than being just a barrier towards something better, then players will exploit it until curiosity kicks in. Of course, the player will research certain fields in order to progress throughout the game, but objectives shouldn't be the only reason to do so.
Unlocking advanced blueprints may draw the player's attention and push them to explore and discover more about such items. But it may also become a distraction from the current and spoil the experience you designed because players aren't paying attention to the current game and are just focusing on upgrading that particular technology.
As you stated in the comments, you don't want players to just play around and randomly discover tech combos by themselves. Then, you could bind tech availability and blueprint ownership to prevent game-breaking experiences or "gold rushes" in one's subsequent games. In this case, no advanced blueprints shall be dropped at all, unless there's a valid reason to do so (an alien technology yet to be unveiled, for example). But, you shall be generous with other blueprints, as the player expects to progress faster in a certain field when their research is over.
A linear approach is neither good nor bad: it depends on your game. Complex systems aren't necessarily better, and simple ones can be good enough to get the job done. Remember that simple rules can create complex behaviours like in-game AI or procedural generation. Even if your player owns a handful of tech, the possibilities may be countless and even unpredictable: what if Jump packs and Gunlink make units too powerful? You shall also test and balance these scenarios.