Lots and lots and lots of spoilers here… or are they spoilers? Answering that would be a spoiler.
The most recent episode of The Flash, Out Of Time, would for most shows be a season finale. It contained so many big moments that they've been building up to for month… and then took them all back. They let the proverbial cat out of the bag and then coaxed him back in. So where the following are important moments they also might not be. That will make sense if you've seen the episode… and if you haven't, then go watch it. As for the important moments.
1) We start with the night the Clyde Mardon killed Joe West's partner and then escapes in a plane with his brother Mark Mardon only to be taken out by the blast from the particle accelerator. Besides it setting up for Mardon to come hunting the cop that killed his brother later on… it also shows that two people in the same place at the time of the explosion could end up with similar powers. Mark's control is much better than Clyde's, but that could be from practice or from where they were in the accident. Either way it adds an interesting dynamic to the show that can be used later on.
2) The accidental double-date at the bowling alley demonstrated to both Eddie Thawne and Linda Park that there is more between Barry Allen and Iris West than anyone is saying. Regardless of what happens in the rest of the episode, Eddie is not happy with what's going on with Iris and Barry which could become very important later on.
3) While running to the morgue, Barry sees another version of himself. He doesn't understand it and goes to Harrison Wells for help, but they have to put it on the back burner because of Maron going after Joe. This becomes incredibly important since everything that happens after it gets erased. And only the thing Barry knew about will be remembered. So Captain David Singh getting hit by lightning and possibly never walking again… undone. Barry and Iris kissing… undone. His identity reveal… undone. That thing with Dr. Wells and Cisco Ramon… undone.
4) So… that thing with Cisco… he's too smart for his own good. He starts digging into why the containment field failed when they had Reverse-Flash trapped and he finds a recording that shows an image of the Man In Yellow, which shows he was never there. Wells walks in and comes clean. He admits he is Eobard Thawne, a distant relative of Eddie's and the man who killed Nora Allen… though he was originally planning to kill Barry Allen instead. But he got trapped in this time and has been stuck for fifteen years… now he's trying to use Barry's speed to get himself home. He of course can't let anyone know about this, so even though he thinks of Cisco as a son… he kills him.
5) To stop a tsunami conjured up by Mardon, The Flash starts running up and down the coast as fast as he can trying to make a wall of wind. In moving so fast, Barry rips a whole in time and space and ends up running next to himself as he had been just after the double date, but this time when he stops, its the Barry from the future. Now this is a big moment for two reasons and the first is… time travel. In the Flash comics the three big things are the Rogues, the Speed Force and Time Travel. We've got a lot of the Rogues, we've had hints to the Speed Force with Wells talking to Gideon and now we have time travel.
6) The other important thing about traveling through time and taking over his body from the past is what I hinted at before… all the things were undone and now he can change how the day goes. He know when Mardon is going to show up at the police station and can be waiting for him. Preventing Singh from getting hurt and never letting Joe get taken. But he also knows how Iris feels but Iris doesn't have the imminent threat to her father to make her realize it. And most important, Barry never learned about Wells' confession and killing of Cisco. So now Cisco is alive again and unless he gets lead down the same path as before, he'll not hear Wells admit to being the Reverse-Flash. So now the audience knows Wells is Thawne and we know he'd be willing to kill Cisco to get what he wants… but none of the characters know.
Pretty smooth move to reveal all of that then take back. We'll have to wait to see next week how much is going to happen again and what will be different. And as you can see, he'll also have to deal with Captain Cold, Heatwave and Golden Glider.