My wife and I are almost caught up on the series. We're about 1 episode behind (not counting the finale tonight). I know Iris dies in the next episode (well...for now...).
I have to say, while the start of the season was pretty entertaining, the Savitar thing has just grown tired. There have been several negative effects resulting from this storyline.
1. Yet another killer nasty speedster who also happens to have a mystery identity. Meh. I'm over this storyline. While it's nice to have Flash fight other speedsters (and appropriate, per the comic), we're at a point now where we're rapidly running out of enemy speedsters. We already did Thawne, Zoom, and Savitar. Who's left?! This story has gotten stale, especially in terms of "fridging" yet another person close to Barry. It's just not compelling anymore. It's old hat.
2. The tone of the series has shifted from the fun, upbeat show it started as to become a far more dour slog. This plagued Arrow's previous couple of seasons (although this season is a lot better). I could accept it on Arrow, because Arrow is a grittier, Batman-esque show. But the Flash really distinguished itself by being something different, and I really enjoyed it. This season, though, it's had the same effect on me that Arrow's near-perpetual glumness has: I stop giving a crap about what happens to the characters. Oh look. Barry/Oliver is sad again. Yawn.
3. The constant use of time travel is hurting the show. We already have a time-travel show in the form of Legends of Tomorrow, which is actually a lot of fun. We don't need another time travel show. Time travel, when it's used, should be something monumental, something truly special and, if not unique, at least extremely rare. Yet on this show, it's become standard practice.
4. The episode where Barry lost his memory, along with the musical episode, HEAVILY reminded me of what the show used to be like, and how far it's deviated from that. It makes returning to the current tone that much more of a bummer. It's not fun. And it simply doesn't need to be this way. In the comics, Barry Allen is fundamentally an optimist. Hell, when Blackest Night happened, he became a Blue Lantern -- the lanterns who embody hope. That's been sorely missing in the show lately.
5. After watching Agents of SHIELD this season, I have to say that I think 10-ish episode arcs are a much better way to go. They can be linked together, but they need to remain distinct. Having a single "big bad" all season long becomes a problem, because you end up having to do one of two things: either you do "monster of the week" episodes in between "story arc" episodes (which makes the "monster of the week" episodes feel pointless), or you have to draaaaaaaaaag out the plot by making the big bads ridiculously powerful, cunning, or capable. The thing is, this ends up getting to a point where it becomes inconceivable that the big bad could be beaten at all. If they're literally always one step ahead of you, if they can always anticipate your next move, and if you spend an entire freaking season trying to catch them and failing to do so, why the hell should whatever you come up with in the finale episode be the thing that actually works? Arrow has had the same problem this season with Prometheus. When you ascend your big bads to near-godhood, you make the ultimate resolution of the story feel contrived because so many other attempts have failed, so why should this one be any different? The problem there is that the plots seem to focus on the big bads being the problem, when what they ought to be doing is focusing on the main cast and their own internal problems as the true obstacle to success. Like, the hero needs to gain a new power, or resolve a conflict within themselves to defeat the seemingly omnipotent bad guy. And yet, it's always some external solution like the Speed Force Bazooka or whatever.
With shorter season arcs, you could present credible threats that don't elevate to the level of omnipotence/omniscience in order to somehow avoid from being caught for 22 episodes.
I actually think this is one of the things that Supergirl has handled best out of all of the Berlantiverse shows. They haven't focused on a single big bad for an entire season. Instead, it's been some monster-of-the-week, but more just about how the characters interact, with one threat eventually rising to the level that they're worthy of a finale (e.g., the Daxamites).
Anyway, I'm really hoping that next season will see an improvement. Arrow definitely improved this season from the previous ones and, while still serious, actually seems a bit more fun. Here's hoping The Flash can reclaim its own sense of fun.