Lacking both as a fighting game and as a crossover. There's a lot wrong with this game and most of it stems from greed and reeks of cut corners. Under Night characters got new art and RWBY got brand new sprites and art, but this is only because they didn't have pre-existing ones. Everything else is reused assets. None of the reused soundtracks were remixed and there's not much in way of original tracks.
Story Mode is basically a bad Chinese knock off of Persona 4 Arena. Characters only have one portrait (not animated), everyone keeps losing the plot, and the main antagonist basically has to force initiate almost every fight. Main antagonist is boring, repeats herself often, and is overall underwhelming. Plot is barely there and nothing is explained. Character interactions were good, but too short. Some pairs who could've had amazing interactions had none whatsoever.
The game is lacking in content (ex: no arcade mode) and updates very infrequently. Gets boring fast and has low replayability. Hardcore fighting game fans will probably find the simpler combos and high damage outputs make the game too easy. The roster is horribly unbalanced character-wise and small for a 4-way crossover. Breakdown: BB has 19 reps in total, RWBY only has 5, while P4 and Under Night have 13 and 12 respectively. For a 4-way crossover with tons of usable characters from every series this sure does feel like a tiny roster.
Was hyped when it was announced, started to get worried with the shady DLC, and ended up hating the "finished" product after playing it. This feels like a rush job to make money fast and to release in time for EVO. Feels like it needed another year or two in development. Would not recommend.