(This writeup is just of the third season; I watched (and liked very much) the first two seasons back when they originally aired close to a decade ago.)
"Why did this need to come back?" This is the ur-question every television revival must answer, and most fail to do so beyond "because the cast was available, because it was easy IP, and because the network is intellectually bankrupt."
I don't think Party Down had a particularly satisfying answer to this question — you could really stretch and say something about how the first two seasons of the show are largely around people who think they're on the cusp of making it despite that cusp having passed them by many years ago, and how that text interacts fairly interestingly with the large amount of success that the cast has gone on to have in the following years, but it's not a question the show is interested in answering after the first episode 1.
The key difference, though: Party Down still has its fastball. The cast (including newcomers!) were terrific and comfortable in their old roles; the scriptwriting might have been even better than its original run. (Most notably, the show was able to do a first-ever in my book: a "everyone is on drugs!" episode that is actually funny!)
It was a short season, and ended on what felt like a bit of a different show (one with more traditional, sit-commy instincts) but it was a fun ride and I'd be excited for another season.
There is some stuff on the margins around Scott's character being truly at home in this world as opposed to in Evie's, but that felt like a hackneyed plot device. ↩