In my review of "Slaine:Lord of Misrule" I said I didn't like the time-trevalling aspects of Slaine and the Slaine vs The Normans was too anachronistic. This is Slaine vs The Romans, but it works much better.
I agree with the previous reveiwer that this is not as good as "Horned God" but its still profoundly Celtic and suprisingly educational. Pat Mills is far more clearly on a mission to do justice to the celtic/pictish mythos and inform the reader in these somewhat unrelated tales than in the more recent Slaine. The humour is also fresher and subtler in early Slaine. The villain, Elfric, is not one of Slaine's best foes and hard to take seriously. Having an unmagically assisted mechanistic and disciplined Roman occupation machine would have been more effective I think.
The artwork (Glenn Fabry, Gregg Staples, Dermot Power) is good. It feels more timeless than Langley's later photoshoppery. Fabry's is particularly intersting, a sort of "fantasy noir".
No interesting extra materials. There is "Cauldron of Blood" from the Slaine Gaming Book but a printing error results in the instructions appearing twice and the first page of panels omitted, which is irritating. Also 5 covers/"poster" pages which are nice but no big deal Some Pat Mills commentary on the relevant history would have been far more welcome.
But overall: if you already have Horned god and either of the first two Invasions books, this is probably the best next Slaine to buy.