Stellaris is a decent enough game but I don't think the comparison to MOO2 is particularly apt. Right in this thread you can read people talking about MOO2's quirks and deficiencies or the fact that they still play it - this, to me, says something about the strength of its design. Stellaris, conversely, doesn't even have a static core design - the game changes drastically with every expansion. It's more of a sequence of related games, some better than others, using the same engine.