Tech tree though seems a bit limited, though much bigger than any RTS I've seen. Did I understand correctly that other races have other tech trees and units? I'd imagine that it's easy to research the entire tree on a bigger map. This makes me suspect that a bigger map with slower play is not what this game is designed to do well.
Yeah, the tech tree hasn't the scope of your usual 4x tech tree and your correct that on larger maps you'll most likely have researched everything important about mid-game.
But you can easily change some of the research items by moding some numbers to expand the tree significantly. (I for example have made all end-tier weapons, shield, hull, culture, etc. upgrades go up to lvl 99 so I always have something to spend my ressources on on very large maps.
Still not quite sure what the papers-scissors-rock is for this game. That's because I don't know for sure yet when a unit (especially pirates) is a fighter, a small ship or a capital ship and it's not clear to me from the unit descriptions what units are good against what units (especially: which squadron type to use against smaller, I think frigate-sized, ships)
Diplomacy seems a bit weird. Is there a way to offer "missions" to others instead of just receiving them?
Yeah, diplomacy sucks a bit, it's just a bit over your usual rts diplomacy so not really good.
As for the rock, paper shotgun system you can hover over the ships icons in the construction menues (as in the squadron build menus) and it will give you a good idea what's strong against what.
As to find out what type of ship is what class playing each race would be the easiest to find out. But basically each race has a light frigate, it's just not called that for every race. For the Advent the name is Disciple Vessel and the Vasari one is the Ravastra Skirmisher. Also each race has a long range frigate, an antifighter frigate, etc.
As to find out which ones are capital ships, that's easy. The large ships that kill your smaller ships in droves, those are capital ships.
For a game with this much graphical sauce, the ships seem just a bit too small. Weird.
That's inherent to the zoom system used. In SupCom for example it's even worse, most units there appear really tiny since you can't zoom that much in to make them appear large.
If you zoom into the ships they'll appear large enough but then you probably won't have a playable field of vision.
From the demo, I obviously have no clue on the other races. Are they different enough? I mean, like StarCraft-different, though still balanced? Or just like RoN-different, with a unique unit or two and some race-specific bonus?
They aren't StarCraft-different, but they're different enough. Each race has the same unit concept but with different executions.
For example each race has a light frigate, but they all cost different amounts of ressources and aren't the same strength. Differences are mostly from capital ships and their abilities (which are very different between each races) and the support cruisers with their abilities and some differences in structures/culture and fighter/bomber powers.
This means that while each race has a unit to roughly correspondents to the other races unit the fleet mixup is stilly quite different because of the supporting abilities you get for your ships are very different.
The Advent for example have quite cheap ships with low hull and armor ratings but very powerful shields and higher shield mitigation. They also have a good capital shield which can easily refill shields to complement that ability. The Guardian support cruiser also has an ability that lowers all damage by a third by taking part of damage done to nearby friendlies on its own shields.
One more thing, added to this: I have a slight fear that battles may degrade a bit into "ping pong" because it's rather easy to guage if you'll be able to win an encounter, thus leading to endless chases. Paradox gamers here will know what I'm on about. Is this a likely scenario?
In multiplayer, yes. Whack-a-mole is a problem.
In singleplayer it isn't that much of a problem, because if you fortify a planet enough the AI usually won't bypass it like a human player would thus giving more or less stable frontlines to fight at.