Solo: A Star Wars Story is a trifle. Solo is a puff pastry of a movie. Solo is a lark. But none of those things are inherently bad, and in fact they’re kind of refreshing. In the main Star Wars saga we get movies about the big, dramatic moments in galactic history. In Rogue One we got a movie about a small but vital moment in galactic history. In Solo we get a fun heist with some enjoyable double crossing and reversals that has plenty of connections to the larger Star Wars universe but that is more interested in exploring small parts of relationships rather than big pieces of canon.
It definitely feels like a prequel, but not to Star Wars; Solo ends in a way that seems to be setting up a major storyline for some future media (a sequel? A cartoon? A series of comics? Masters of Teras Kasi 2?), and it expands out the criminal underworld of Star Wars enough to offer space for all sorts of other spin-offs. There is always a small universe problem plaguing the Star Wars films – everybody talks about the same six planets, after all – but I actually think Solo carves out enough new space (and illuminates existing space in enough interesting ways) to give the Star Wars universe a little extra breathing room.