I watched the anime before reading the manga, which might color my view. The visuals and action sequences are its strongest suit, especially the demon weapon animations and the large-scale battles. Yuichiro's rage-fueled drive is captured well, and Mikaela's introduction has a decent impact.
Where it falters is pacing. It adapts the early manga arcs which are heavy on setup—the human-vampire conflict, the mysterious virus, the political machinations within the Japanese Imperial Demon Army. The anime tries to cram a lot of world-building into 12 episodes, so some character motivations feel rushed, and the middle section can drag. The ending is also a classic 'read the manga' non-conclusion, which was frustrating at the time. If you're cool with a stylish shonen that sets up a bigger story it doesn't finish, it's a fun, if flawed, watch.
I'd say it's worth a shot if the premise intrigues you, but temper expectations for narrative depth.