The story was a bit of a mess, as is usually the case when these shows try too hard to weave a tangled web with too large of an expansive cast of characters. Similar gripes to be found with Arrow and Supergirl, to be sure.
The cast and their performances keep this from being a total dud, and the special FX in the episode were pretty strong. I like that Barry rebelled against the propensity to "go dark" and tried to appeal to his doppleganger's heart.
The ending just seemed tacked on to force us into a cliffhanger. Yes, Barry ultimately was responsible for a lot of things going wrong this year for a lot of people. But sentencing him to an eternity in the Speed Force as a result after he had just worked his tail off to set everything to being as right as possible seems odd. And this whole "Speed Force Prison" concept is just utterly insane as well. There has to be a Speedster in there at all times? What about before Barry locked Savitar in there in the first place?
Anyway. We'll see Barry again, I'm sure. The Speed Force is a sentient entity and I'm sure it will come up with some "purpose" for Barry in terms of allowing him back out. But in the meantime, it looks like Kid Flash is Central City's new hero. We'll see how he does.
No Speedster villains with shocking secret identities in Season 4, please. Personally, I would love to see more of the Rogues' Gallery - Captain Cold, Heatwave, Grodd, King Shark, etc. etc...having all of these people be a thorn in the side of the Flash and Co. and generally having the show feel more like the fun comic book it did in the first season would be refreshing.