Okay, I've given it 3 listens too.
Here's my take:
Panic Attack - Completely agree with everything you said. The best opening track on a Priest album since Painkiller - it's really that good. 10
The Serpent & The King - Solid track #2. I don't see it as weaker than Panic Attack, as it's a totally different kind of track. I wasn't a huge Firepower fan except for 2-3 tracks, but Panic Attack and TS&TK alone are better than anything on that album imo. 9
Invincible Shield - One of the best on the album - sounds like a cousin to Panic Attack. Chorus reminds me a bit of Redeemer of Souls, but overall this song has way more bite to it. And yes, the outro is classic Priest. Great track. 9
Devil In Disguise - Sounds very 80s Priest to me. I especially like the riffing on the pre-chorus. The chorus isn't the best, but kinda fun if a little throwaway. 5
Gates of Hell - Fans seem to really dig this from what I've read so far, but it hasn't really grabbed me tbh. Chorus is good I suppose, but it doesn't move me much. 6
Crown Of Horns - This has been a grower for me. I wasn't keen at first, but it sounds better with repeated listens. A bit MOR, but not everything has to be Panic Attack. 7
As God Is My Witness - Very Painkiller-esque. Great energy, cool solo, I like this. 7
Trial By Fire - An obvious single choice, very catchy. A bit "safe", but hard not to enjoy. 7
Escape From Reality - This is good. Great main riff. The middle-eight section sounds just like Ozzy Osbourne - seriously if you'd have played me just that part, I would've said it was Ozzy singing, not Rob. 8
Sons of Thunder - Has a good energy. Verses sound like they have potential but the chorus isn't great. 5
Giants In The Sky - I like the sentiment and Rob's big powerful vocals at the end are cool. Love the Spanish guitar licks and Rob's melody lines throughout. 8
Fight of Your Life - I like this, it isn't amazing or anything, but I love Rob's vocal delivery in the verses - I love it when he uses that tone. Reminds me a bit of the way he sings Deal With The Devil from Angel of Retribution. Solid chorus too. 6.5
Vicious Circle - Sound very "bonus track" quality to me. Unremarkable. 3
The Lodger - I really like this, if only for the fact that it sounds totally different to anything they've done recently. I also like it when Priest embrace storytelling in their songs, but then I was one of the few fans who thought Nostradamus was a masterpiece.... 8
Overall - Decent, but it'd be stronger as a 10 track album as the second half really doesn't live up to the first half. If only the rest of the album lived up to the opening three tracks. I gotta say, I miss KK. I may be in the minority here, but albums like Angel of Retribution and the criminally-underrated Nostradamus pack far more of a punch to my ears than any of the post-KK albums have. Having said that, I do prefer Invincible Shield quite significantly to Firepower. I would put it perhaps on a level with Redeemers - 3 or so fantastic songs, a bunch of solid ones and a few duds. For me, Firepower was just middling beginning to end, not bad, but nothing spectacular (Traitors Gate raised a pulse, but that was the only one, really). My main gripe is that it all sounds very "safe" to me - I feel like they really pushed themselves on Nostradamus to do something different and progressive and because some narrow-minded 80s metalheads wet their panties, the band have been playing it safe ever since. I know they never will, but they really should give KK a call.