While it sounds like an interesting book, I found Richard James Bentley's Greenbeard to be disappointing. I blame this on the book's description, which makes it sound weirder and funnier than it actually is. Don't get me wrong, it's not bad; it's just not as good as I was expecting.
The titular Greenbeard, aka Sylvestere de Greybagges, is a lawyer turned pirate captain who used to have a normal bear until he was enslaved by an alien being who gave him a green beard so he could serve it better. Being a pirate, he naturally managed to escape and vowed revenge. Most of the book deals with him turning his pirate ship into a space ship, and only the final few pages deal with his actual battle against alien forces.
He has plenty of adventures along the way. He manages to rescue a "Frank Banjamin" from Barbary pirates who had enslaved him, and as you might guess, Mr. Benjamin seems to be Ben Franklin with his name changed for no apparent reason since other historical figures appear with their real names. He also meets Solomon Kane, whose name is changed Solomon Pole, even including a parody of "Solomon Kane's Homecoming," despite the fact that Robert E. Howard wouldn't have written it for more than a century after this book's time period. The book does involve time travel, though, so I suppose that might explain this particular anachronism, though I personally found it annoying.
I also found the Lovecraftian name dropping annoying. The alien who kidnapped Greenbeard is apparently one of the Great Old Ones, and Cthulhu is mentioned--as is Mrs. Cthulhu and their daughter Lulu Cthulhu--but these seem to be Great Old Ones and Cthulhu in name only. They lack any of the cosmic terror of Lovecraft, and are just kind of lame.
Obviously the Mrs. Cthulhu and Lulu Cthulhu are intended to be humorous, but it just kind of falls flat. In fact much of the book seems to be intended to be witty, with references to philosophy, and many bad puns. At times it almost felt like I's wandered into a Xanth novel.
This just really isn't for me. It's not weird enough for weird fiction. It's no where near funny enough for humorous fiction. The plot is a bit too slow for action fiction. Even the science fiction aspects are kind of lame.