"Season 9" really is the start of a spin-off show. Some cast members stay (Turk, Cox), some stay for a short while (JD, janitor) some are gone entirely (Carla,...).
As far as closure goes, you're better off staying with Season 8, which has an actual finale. Season 9 just peters out all of a sudden. If you're buying this to see the end of the Scrubs story, well, it doesn't really give that.
If you're interested in a show that's loosely related to Scrubs, in the same universe, but with different characters, it's worth a shot. Some characters are very much "replacements" of others and fall short of the norm (Sorry, Security - Janitor was better), others are variations on a theme. My main problem with the season is probably that the main character and her (later on) boyfriend aren't the most easy characters to feel connected to. Lucy's "the insecure girl" as much as JD was "the insecure boy" in the first season, but of course "even worse". Her boyfriend's an entitled jackass who, I guess, would slowly learn to be a decent human being? We see some small shreds of this but the show's too short for all that much growth...
A) It's not really a continuation as much as a spin-off
B) The characters are, overall, a little less interesting than those of the original
C) The story line and jokes are on par with the later seasons of Scrubs. Don't *quite* hold up to the earlier seasons, but still quite enjoyable.
D) The season's only 13 episodes, which means that, especially introducing a bunch of new characters, it's a bit short.
E) In general, this is a bit less good than the "original" Scrubs, but it's by no means a bad series; unfortunately axed before it got off the ground, partially, I suspect, because people went in with wrong expectations (see also: How I met your Father, That 80s Show,...)