This version of Spelljammer is leaning a lot more into the sci-fi influences than the previous, but it is still D&D in Space. The biggest draw of Spelljammer is its expansiveness. You can have cohesive adventures that explore many different cultures and styles without seeming a kitchen sink or mish mash. Do you want to run a Master and Commander style wartime exploration? Easy as pie. Pirates of the Caribbean? Got you covered. Indian Jones treasure hunting to a variety of locales to find fortune and glory. Sure thing. All those times you think of a great adventure ideas and stories that wouldn't fit in your current campaign, in Spelljammer they can fit without it being jarring.
There is a lot of gonzo in Spelljammer. Giant Space Hamsters, explosive loving British Hippo people, Space Clowns, weird physics and gravity... but they don't have to be emphasized. You can run tense, horror-filled thrillers or engaging character-driven dramas without using the weird elements like any other setting.
As for running low-level adventures, it is very easy. The PCs may not own their own ship, but they can be guards/crewmen/specialists for someone else. They can be passengers going from one point to another. The foes in Spelljammer come in all Challenge Ratings. The Astral Sea could be super powerful or mostly empty but it is a means of travel, like the open ocean.
Why do I like Spelljammer? I love running an adventure where the party is struggling to fight off a crew of skeletons from a derelict Hammership while trying to salvage the Spelljammer Helm while avoiding an Imperial Elven Navy Man o' War patrol in an asteroid belt. There is swashbuckling, wild west, and Napoleonic wars mixed together with giant sea creature-shaped ships flinging cannon and fireballs at each other. There are mind flayers in nautiloids, beholders trying to assert individual dominance in crazy personal ships, and planet-eating weapons of mass destruction.
