It's not bad per se, and as a matter of fact I think all individual novels, novellas, and short stories rate around 4 stars for me. Yriel, the Harlequins, and the Blood Angels stood out as great characters and Dread Night was an epic end to this omnibus.
Additionally, Deathstorm by Reynolds deserves an honourable mention as my favourite story in this omnibus by far. A POV switch between the Blood Angels and a semi-sentient Tyranid Broodlord combined with an epic story and perhaps my favourite space marine chapter make for a solid 5/5.
Nevertheless I can't bring myself to rate this omnibus as a whole higher than 3 stars. I can't really explain why but it felt like something was missing? It might have been a slight lack in diversity of overall plot (Tyranid scary, Tyranid overwhelm world, [insert faction] embarks on a (semi) hopeless battle against said Tyranids), or maybe just a slight Tyranid burnout from reading this omnibus in one three day sitting.
Overall, I'd definitely recommend this omnibus if you are a fan of either Tyranids, Eldar, Necrons, or the Blood Angels but maybe read it piecemeal instead of as a whole in one sitting.