All the Tony Martin albums are on streaming, and I listened to them all. Thoughts, with pros and cons
The Eternal Idol
Pros: RIFFS! Iommi sounds pretty inspired, and the songs (The title track-which is like a darker version of "Born Again"-"Ancient Warrior" and "Hard Life to Live" are highlights) can be pretty catchy
Cons: Martin's voice-which isn't bad-hasn't found it's place. Also, as an album it's fine, but it feels like somethings missing-Iommi's great, but everyone else sometimes feels like a work for hire (which they are TBH)
Headless Cross
Pros: Uh, this is actually really good-hell, at times great. Everyone's finally found their groove, Martin is clearly more comfortable (he sounds like the singer for an Epic Doom or early Power Metal band) and truth be told, there isn't a weak song here. Also, the title song is great, and the record at times sounds as influenced by a few bands they inspired (stuff like Candlemass, Solitude Aeturnus and St Vitus for example)
Cons: Synths occasionally don't feel necessary. Otherwise not many.
Tyr
Pros: Most of the songs here are good to great-"Anno Mundi" in particular deserves to be considered a Doom classic, and vocals wise this might be Martin's best moment with the band. The man really sings his heart out.
Cons: the Power Ballad "Feels Good to Me" is a bit too schmaltzy for me, and feels like it belongs on a different album.
Cross Purposes
Pros: This has a negative reputation among some fans? Because it largely feels inspired. Butler returning clearly has Iommi giving a hell of an effort, and there's some great riffs here-especially on "Virtual Death" and "Evil Eye"
Cons: Martin's performance isn't bad, but he feels-less inspired I guess (considering he was let go for "Dehumanizer" and then was asked back probably doesn't help). Here he just sounds like a metal frontman.
Forbidden
Pros: One of the biggest complaints about this album has always been the mix, which was muddy and unappealing. Iommi's remix of this (and the prior records) is a minor miracle in that you can actually hear the band better and it's much clearer. "Get a Grip" and "Kiss of Death" are actually good.
Cons: It's still "Forbidden". This means that it's the "Never Say Die" of this era, where the band sounds at odds with one another and don't seem to want to be making the album. I still don't know why Ice T is there other than Body Count.