I've played through a patchwork of Missions over the years.
I liked Season 1 well enough because it's set in Seattle and I'm from Seattle and I liked to local details. That said, it used 3E rules and I was playing through it with 4E and 5E so I had to do some adapting. I liked Season 4 for the same reason, but since it was 4E I didn't need to adapt it as much.
To Iduno's point, Missions are very session-based and not very open-world. You generally won't find treacherous Johnsons and backstabbing contacts in Missions, nor will the modules explore the downtime between jobs. They'll be missing some of the character of the Sixth World as a result.
Another catch is that they're written around the "lowest common denominator", which is to say they're written for conventions where you never know what combination of PCs you'll have at a table. You could have four technomancers or no Matrix support whatsoever. As such, Missions are usually written in a fairly straightforward way that can be resolved without the express need for magic or Matrix. Those can often help but they won't be necessary. In other words, Missions usually focus on the physical world. There's almost always a fight available, although in some cases it can be avoided. (I played in one where we sidestepped a fight through good planning, good rolls, and the luck to have all the right skills and tools available.)
Depending on what edition you're playing, one of the nice things about Missions is that their FAQs (
here) can function as errata and provide a bit of game balancing, outlawing some of the more outrageous possibilities. This is especially true for 5E and 6E.
But if you're a GM without a lot of time in your life for planning, where you just want a script to read and goons with stats, the Missions can be a great fit.