The Series One's have only just been released so in depth reviews may be a little hard to come by.
Guitarist magazine in the UK managed to get hold of one of the protoypes a couple of months back, and they loved it.
http://www.musicradar.com/gear/all/amplification/instrument-amps/guitar-combo-amps/series-1-s1-45-combo-212014/review
All of the 'Big Boy' Blackstars, are getting great reviews from everywhere.