Like the Sunday Funnies...
Poor Swamp Thing - not only can he not get a break in his (fictional) life, he can't get a real one in print either.
His own series was canceled after only 24 issues, then he got a starring role in Challengers of the Unknown only to see that series canceled after appearing in only a handful of issues.
Which leaves him making guest appearances playing second fiddle to other heroes, like Batman in Brave and the Bold, and Superman here. While this issue isn't as annoying in some ways as Brave and the Bold #122 was, it has it's own set of problems. Namely, that it really dumbs things down to an old fashioned Sunday funnies type story. Swamp Thing finds Solomon Grundy the minute he gets to Metropolis. Coincidentally seconds before Superman. Swamp Thing happens to have an entire lab set up in a Metropolis sewer, etc. Plus, when the art doesn't look stiff and old-fashioned, it's full of corny "Bazooka Joe" style wild takes.
This is like the Vegas years of Swamp Thing's career. Playing kitchy Swamp Monster in comic relief one shots.