I enjoyed both episodes, as always, but it was certainly a different tone from what we're normally used to. Sure, as
@Drtooth has pointed out, the episodes have gotten to a pattern of being cutesy, fun and colourful for the first bit then turning quite dark in the next bit. However, those episodes still ended on a happy ending or, at worst, there was a small glimmer of hope or Steven laughed it off like 'haha that was so weird that I saw myself die.' In Mirror Gem, it turned eerily frightening in a few seconds. The Gems reactions, epspecially Garnet's, was so unexpected. We as the audence were on the same page as Steven. We didn't know why they were acting the way they were, all defensive and 'don't make me take it from you', something we had never seen before. And even after we found out about Lapis Lazuli we were still left in the dark. ****, even after Ocean Gem a lot of things are still vague. This seems to imply strongly that the Gems, the good ones we've got to know and love throughout the show, are perhaps not as heroic as we thought they were.
I hope they explore more of this in the next coming episodes/season. This world they've created got a whole lot more interesting other than being a cute, funny show that channels a lot of anime 90s nostalgia.