Scum & Villainy is the first game I've used to GM a full campaign (as opposed to one-shots or a short series of games). I'm glad I did. It's an excellent game.
Probably the main reason I haven't GMed something longer before now is I struggle to link up plot threads into a larger narrative. S&V provides great tools to assist with this, beginning with the starting situations offered for each ship type, downtime entanglements, and ongoing faction plots that keep your crew engaged.
The rules are a dream. If you're at all familiar with Blades in the Dark/Forged in the Dark, all of the strengths are there. The position-effect-consequences triad is one of the smartest ideas I've ever seen in tabletop, and allows the GM to fluidly progress the session in a way that fits both the needs of the crew and the narrative logic that's been established. The playbooks are fun, and pretty easy to modify if you feel the need. I'd advise any GM to take a look at the advice in chapter 10 of the book if you're likely to consider modding the rules. There are a lot of good ideas here to build on.
The crew's ship became a fun RP hub in between jobs and the ship abilities were a particular strength because our Pilot always wanted to stay behind on the ship (it was an interesting task keeping him in play for every job). It's helpful to consider how your crew's choices during ship creation can fit into jobs as you create them.
If you're interested in playing your own custom setting or even adapting other fiction for use (e.g. Firefly), the rules work very well and most playbooks need little if any modification. However, I'd recommend at least checking out the setting provided with the book. It's a lot of fun!
I'm hard-pressed to think of specific criticisms. My group sometimes skipped engagement rolls or "doubled up" downtime activities to help with relieving harm or renewing stress when the rules felt too restrictive, but I don't think that means these elements are bad ideas; they just didn't work for our group every time.
If you're interested in space outlaw hijinks and prefer rules that stress narrative over simulation, check this one out.