It contains two stories, neither of which is particularly good. Their quiet moments can be nice, though.
The main story is Threads (40 pages). A white fungus is killing people in Gotham City, so Batman goes looking for Swamp Thing. (The fungus resembles Ophiocordyceps unilateralis, also known as the zombie-ant fungus because it infects ants and turns them into walking fungal spore chambers. Its victims climb to a certain height above the ground, then wait for fruiting bodies to grow from their heads and kill them.)
That's a promising idea, but Bissette hasn't really worked out how to turn it into a story. Batman gets infected and wanders around, basically, while Swamp Thing watches. Reading it is a little odd, though, because this is the 1988 annual and hence only a year since Alan Moore's famous run on the series. Its continuity references are all to things Moore wrote. Batman last met Swamp Thing when Abby had been arrested.
It does, though, have one emotionally resonant page towards the end. A homeless lady got infected and she's being looked after in Gotham Clinic, unaware that she's going to die. She's been given a room with a TV. She watches a movie about someone called Apple Annie. "'Higher', her mind whispers. What life-style could be ritzier than this? How higher up the social ladder could she climb? But what good is it, with no one to see her? It is warm, and comfortable. She has all the food she could eat. But she is so lonely. It is as lonely as life on the street had ever been. She cries a tear for 'Apple Annie'."
There's also a cool Swamp Thing tree transformation on p32.
Bizarrely, though, the last page tells us that the fungus is called Matango, in a reference to the 1963 Japanese horror film about infectious killer mushrooms.
After that, there's an eight-page back-up story about medicine men in the bayou. That works better than the main story, because it has no action and is just a pastoral, character-based piece.
Overall, this annual's on the borderline between "keep" and "throw in the bin". I've bought it. It doesn't take much space. But it's not much good. I'll probably keep it, though, because I love Alan Moore's Swamp Thing and this has strong connections to it.