This episode is a classic Season One mixed bag - some great ideas and some terrible execution. On the plus side, we have John's "time-flashes". Getting a glimpse of your (possible) future is a classic sci-fi trope and it works well here. The episode doesn't play fair though - at first the time flashes have a visual effect associated with them, so we know that John is having them. Eventually when they start getting longer and more elaborate, there is no transition. It just seems like normal action up until the point where the timeline gets hopeless, then, boom, we're back before it all happened. It doesn't matter though, this part of the story works, and is quite entertaining.
On the negative side, we have the guest actors. Matalla is terrible, with the sort of mannered affectation that has ruined a lot of the alien guest stars so far. Unfortunately she's a rather large part of the episode.
I am a sucker for time-travel shenanigans though, and this episode has them in spades. It's worth watching for that aspect of the plot alone.