I believe Rome's real "conquest" was in the accomodation of subject peoples. The propertied classes could become part of the ruling hierarchy, and the military veterans were granted citizenship. Everywhere a Roman "consumer culture" sprouted. And then of course there was the later grant of nearly universal citizenship. Turning subjects into citizens and junior partners of the commonwealth in which they had a vested interest is something that few empires before or since have done so well - or even had the inclination to do.
Really, if Rome were just another expansionist state that conquered, collected taxes, roughed up the locals, and then collapsed, why would I care about it any more than the Assyrian Empire, of the Golden Horde? For me it's not about which group of soldiers killed another bunch of soldiers on some desolate battlefield - it's about culture, identity, civilization. If Rome hadn't turned other people into Romans and laid a critical building block for what most of us call "Western Civilization" I really wouldn't care.
Rome was great because it allowed other people to share in its riches and glory. It allowed other people to define (to some extent) what meant to be Roman...