Example: Eclipse, which we play whenever we find time and people to spend 7-9 hours for a single game. Just starting to play would not really work here, because you can not easily play multiple games to learn the rules incrementally.
That said, Eclipse is currently my favorite game as it's fairly complex, but the goals are laid out pretty simply: Collect victory points (VP), everything with a golden shield with a number gives you VP.
From there it's mostly about teaching the players about the actions they can perform each turn (of which there are six) and the associated costs. But in the first turns everybody will use a single action (explore) so the learning ramp starts of manageable. The move and the upgrade actions are not relevant before ships where build, complexity builds up over the game.
Also: Complexity arises from having a whole load of researchable technologies and discoveries on the board. But all of those are introduced slowly while the game progresses.
All of this falls out of the window when you play with the alien races which changes the rules for every player ... which is why play all humans whenever we have new players at the table.
Long text ... I just love that game ;-)
It takes a little more time to replay the start of the game, but if people are in the spirit of it, the exploration phase of it can move quickly. You don't have to try to make the right play. Just try something. If there's a thing in the rules that can happen, do it and see what happens, even if you think it's probably not the right way to do it.