In my opinion, this particular Dio album is criminally underrated. Dio's vocals are great, as always. Rowan's guitar work is outstanding for someone who was 18 years old at the time. Considering that this album's working title was "metallic blues", I would say it very much lives up to that name. The album has great dynamic range (an average of 12dB's of dynamic range) for the time and is excellently recorded. It is indeed a shame that Dio chose not to continue this lineup.
The only album I would rate higher than this would be Magica.