I've had nearly all the Shivas.
They're great for 90s hard rock stuff like Tool, AIC. Kinda does the Marshall/Mesa combined tone really well.
Great clean channel. Frustrating drive channel with rounded off pick attack and a covered sound until really cranked. The 20th improved on this stuff, but lost some of the good stuff the original has.
They're fine if you're the only guitarist, but get buried if there is something like a Fender Bassman or Marshall in the mix.
The Naylor drive channel is everything I wanted the Shiva to be, and then some. Much better feel and sound.
The 3534 blue channel set to neutral with gain cranked is not dissimilar to the Shiva in attack. But the blue channel sounds and feels better, imo, and the boost is more useful.