I like Eclipse, and I'm thinking about getting this... but I have one question.

Is combat simultaneous?

In Eclipse, I hate, hate, hate that massive groups of ships can get blown up before getting a chance to fire. Same thing in this game or no? I love that in Rebellion they stay on the board until the end of that firing phase.

Get it. Yes combat is simultaneous. If you like rebellion you'll love TI3, it's a little longer but more fun (in my opinion)

Rules aren't super complex - there's just a lot of them.

but there's precombat fire. i never play eclipse but at least here is not that common and mostly is focus in one particular tipe of ship

As has been mentioned, there are a couple special rules that can allow a unit to get in some shots without return fire, but for the most part it's "one side rolls attacks, total hits, other side rolls attacks, total hits, then both sides remove casualties. Then do it again.

If you've ever played axis and allies, the combat system is virtually identical.