In The Nightside Eclipse. It is more closer to traditional black metal and the synths give an eerie atmosphere Anthems just couldn't do. Anthems still has great riffs and is more devloped in the guitar playing but Nightside Eclipse has better riffs and better songs overall.
The stuff that came after Anthems isn't garbage, it's still good music, just not as consistent as the first 2 albums, still there's great songs in IX Equilibirum and Prometheus.