The term 'Power Metal' didn't even existed at the time this album hit the market: this was simply called 'Symphonic Speed Metal'. While Accept did compose the first Power Metal song ever ('Fast as a shark' on 'Restless and wild' album; the rest of the album was in the mainstream of heavy-metal), Walls of Jericho is the first abum that can be called 'Power Metal'. True, there are a couple of songs that are more 'Heavy' than 'Power' ('reptile' and 'gorgar' to name them), but as a whole, it's pure Power Metal. Their music have greatly influenced bands like Blind Guardians, Stratovarius (while there is a not so 'subtle' influence of Yngwie Malmsteen in this case), Sonata Arctica, Angra, Nightwish and every Power Metal group worth his salt.
If you like the Pre-Power Metal era, you would like to know that another group was father of this kind of music: Iron Angel. Of course, groups like Iron Maiden influenced this kind of music, but they have never done Power Metal.
Well, this is it. A perfect album (almost). If you're into metal, you must listen to it...'if you're not into metal, you are not my friend' (Manowar dixit).