I used to do research at the Shedd Aquarium. After watching a particularly clever octopus defeat every attempt to prevent him leaving his enclosure at night, I am absolutely confident that, just like certain aquatic mammals such as Orca whales, that we only devalue their intelligence because they were unfortunate enough to not be in a situation where they could develop significant tool use and the cultural artifacts that said tool use and creation enables.
In previous threads on this topic I don't think I've explained deeply why I find their defeat of our team so impressive. This research group contained a multidisciplinary set of scientists. I was the only member that did not have a PhD; almost every team member had completed at least one significant postdoc as well (think Stanford, UChicago, Caltech, prestigious national labs, etc). We had applied science and engineering talents in addition to pure science, so this wasn't a case of not being able to develop realistic escape prevention mechanisms due to the team being too theoretical. The longest we were able to stop this clever guy from escaping with one of our implementations was 4 days. He usually made us look like idiots the very evening after we installed our new prevention device.
Not only this, the octopus made very clear that he had an extremely well developed memory. He clearly recalled his favorite scientist who hadn't visited in a few years when, as soon as said scientist entered the room, the octopus ignored the rest of us and followed him the entire time he would be in the room. He also became what I can only describe as depressed when that individual departed once again; this was a period of time when he stopped eating as much, moved much more lethargically, and his escape attempts were half-hearted - this was the period when he finally took more than one day to break our attempts at keeping him in.
Further, he absolutely had a sense of humour. After seeing us crack up laughing at him wearing this plastic rings we had put in his tank as jewelry (we were setting up some sort of exam that I can no longer recall the purpose of) by placing them on his tentacles, he would do so every time we entered the room. Otherwise, he ignored the rings entirely when we were not present.
I did not eat octopus prior to this but I became firmly in support of encouraging everyone to avoid eating octopus and related creatures after this experience. Not only do I think they're immensely intelligent animals, I am firmly convinced that this particular specimen was smarter than a number of humans that I have met.