It's pretty cool, as you'd expect from Gaiman. It's also a Swamp Thing annual without the green guy himself, who I think was dead or time-travelling or something in the monthly comic. This works better than you'd think.
Again, there's a long story (Brothers, 42 pages, Rayner/Hoffman) and a short one (Shaggy God Stories, 10 pages, Mignola).
Brothers does a bunch of nifty things. Firstly, it resurrects an obscure DC character, Brother Power the Geek, the protagonist of a two-issue run of a comic in 1968. This is cool because Brother Power was a hippie and that's the main thing Gaiman's talking about here. They called themselves flower children. This is Swamp Thing, a comic about the elemental god of plants. This is such a perfect fit that I wanted Gaiman to turn this into a year-long series just to talk about that. "I saw all the flower children gone to weed and seed and thorn."
Furthermore, one of the series's ongoing regular characters is Chester Williams, card-carrying hippie. He was originally introduced to the series with his discovery that Swamp Thing's tubers were hallucinogenic. He's the perfect counterpart for Brother Power, but also for the hippie-hating black ops agent "Gideon Endor".
There are superheroes. Batman gets a cameo. Firestorm gets more than that, letting Gaiman get lyrical (and comedic) with the strangeness of a superhero.
It's gentle and very good. It's got things to say about the Chester-Liz relationship. It's not what I'd expected, but I like that.
As for Shaggy God Stories, that's fun too, albeit mostly just dialogue. Jason Woodrue goes to visit the Parliament of Trees, though, and it's drawn by Mike Mignola, so it looks good. As the title suggests, Woodrue speculates about plant elementals and various world religions. He also talks to a pot plant. "I'm discussing comparative theology with him. He's not very well educated."
I enjoyed this. It's talky, though, so don't expect cool action and traditional comics finales.