If you liked FE3H for it's story and were expecting another immersive story telling marvel, you're going to be very disappointed. This is a game that focuses on the mechanics and despite its amazing animations, if you play with those turned off it's probably one of the lower rated FE games to date. It feels like they just rushed to get something out following Three Houses an Three Hopes to keep people interested and I feel while Three Houses grew the fan base and was a great introductory entry to the series for new players, this will achieve the complete opposite. Boring story, no NG+ at launch, and impossibly high costs for most of the features in the game like inherited skills from emblems (some costing several thousand more SP than you'll ever be able to earn), and donations to countries for bonuses that will leave you completely broke if you try to max out a single one.
The post-game Engage *does* offer is such a complete waste of time I feel bad for the team who worked on it. Not only do the benefits not carry over because of the aforementioned lack of NG+ but the rewards are a mere pittance for the amount of time needed to invest. Three maps on the highest difficulty setting in a row and rewards scale based on your highest level unit, is if you had hopes of maybe trying out the benched units that didn't get a chance to shine through the story, forget it the rewards for lower difficulties becomes 0 and doesn't grant any experience.
Honestly the game is kind of a joke, the characters are cartoonishly over the top and it's like a 6 year old wrote the story. Honestly the animations and actual combat mechanics are the only thing this game has going for it. As an existing fire emblem fan you'll probably get your money's worth but wow did this game miss the mark. If you can get it on sale, even better, you're not missing anything if you wait.
This may change as the DLC waves come out but even those paralogues to unlock new characters are a slog, with the lack of NG+ if you plan on doing another play through and using them, you then have to complete them all over again. Beyond 1-2 playthroughs the game doesn't offer much else. Maybe their Warriors spin-off will be better.