Stellaris is not a game that I would reccomend. While it seems to offer a wide universe to play in with many different options, this is not really the case. There is a really fundamental problem in the game's design. The most obvious symptom of this is "doomstacks". Doomstacks are how most wars go, there is one battle with all your ships vs all the enemy's ships and once that rather boring slap fight is done, you win the war. The only thing that matters is that your numbers were bigger than the enemy's. Ship design has a MINOR role in this. Unless designs are massively skewed, and they never are, it's just numbers of homogenous fleets.
But why? Lets look at where the game's complexity. It appears to be in its in ethics and government system, you have factions and influence and such. But apart from that? Military, economy and even diplomacy are extremely simplistic and homogenised. Is it any surprise fleet combat is such? It's big numbers v numbers because that's all that matters. Only things that either have a big number or are in large numbers matter. Look at planets, losing one doesn't matter that much in mid or late game. The only thing that gives planets value is what fraction of your empire's energy, minerals, or science they produce. Large empires can easily absorb the loss of multiple planets without really much consequence because they represent a small fraction of their 500 mineral per second income. There's no depth. For such a large game I think Stellaris is actually rather shallow. Things like the endgame crises and War in Heaven (for those with that DLC) are fun, but what are they sitting on? Nothing much really. It almost feels like they're there to distract from the blandness of the normal gameplay.
There were some major complaints with the game a number of patches ago. There was nothing to do. There were no mid game events worth talking about. The game was really hollow apart from the early game rush to colonise, the late game crisis, and final empire steamroll. But that just made me think about how the game is so shallow that it needs such events to remain interesting. Somewhere on the paradox forums the developers have said that they're not interested in making the economy deeper. That has really dampened my interest in the game, as it should yours, because it means this problem will never be fixed.
Other paradox titles like the Europa games game mechanics that aren't massively complex but there's other non-event features that provide depth. In the EU games just having terrain creates actual choices because you need to choose how to deal with it. While income is just ducats you do have choices in how you acquire and spend it. Trade, production, and taxes are all different ways and are still important. You can focus on one, make choices in how you spend your resources to enhance it. Even if you're not focusing on say, trade it's still a good idea to put a little bit of effort into interacting with that system during the game. You can take into account things like the trade goods of resources, how they change in value. You can interact with it with armies, you can scorch the earth and loot places. There's various in-game events that change their values, which change the 'trade landscape.'
Stellaris has none of these things. Planet colonisation is very simple; you colonise, you build one of the three production buildings over the entire surface plus a unity building. In the early game you might take tile resources into account but later in the game the production bonus buildings, and things like assist research mean that you should make your planets produce one resource so you can apply the planetary bonuses to as many production buildings as possible. You have a farm planet(s) too of course but those barely need touching and in any case sectors will ensure that you have more than enough food. Energy credits are near worthless past early game, they exist to be converted into minerals and that's basically it. I'm quite sure you could remove energy credits from the game entirely and there wouldn't be a fundamental shift in the gameplay of Stellaris. Diplomacy is very simple, and has little choice. There's standard pacts, there's federations, but can you demand a planet diplomatically? Can you demand anything, or offer something in support? Can you buy or sell ships? No. Combat is quite simple as we know, but even worse than that is the meaninglessness of ship designs. There are a few designs that are the best and we all know, or soon will, what those are; mono-composition fleets of corvettes or artillery/lance battleships (or whatever the current hotness is). Why build anything else? Why research anything else? Fleet combat is so simple to boil down. The whole game is.
There's very little actual choice in Stellaris. There's no terrain, so you don't need to chose which way to reach your enemies. There's no trade routes so you never choose where to provide value, or what trade good to take control of, and you can never raid trade routes unlike HOI and EU. There's no economy to speak of so you can never choose to focus on this product/component/whatever over another. Even Hearts of Iron has that. As I just said, ship design is an illusory choice. You think you have options but you don't really have meaningful choices. Planetary management has very little in the way of choice, if any. In fact the choices for planets are so non-existent that sectors exist, taking those choices away from you.
Shallow gameplay, do not reccomend. The game looks nice, pity there's nothing worth seeing, certainly not for its price.