Art-wise, my problem with Soul Sisters is that while I love elements of Shaky's work, and love bits of Pinhead Nation and the Soul Gun stories, it rarely looks like the characters have any presence in their environments. The backgrounds and the worlds around the figures looks like a complete afterthought. You look at Kirby, you see surfaces, walls, bricks, etc that all feel solid, with visible textures. Shaky put all his imagination into what his weird characters look like, and not where they are.
That said, I honestly liked Shaky's work a lot more in the '90s. Over time, the shock of the neatness, and just how unexpected it was to see this kind of work in 2000 AD, has worn off, and it just looks like the work of an incredibly imaginative amateur.
That said, the bit in the second Soul Gun story where the two solar-system-sized protagonists start smacking each other over the head with planets really is amazing.