I saw it as simultaneously honorable and insulting. He's conceding that Obi-Wan was indeed a very fine Jedi and a fine teacher as well. But I also saw something sarcastic in there, possibly as a reference as to how Vader felt about Obi-Wan as his own teacher, especially his inability to keep Vader under his wing (something I hadn't thought about until I started writing this post) and also as a slightly disarming phrase (you can see in ROTJ that Vader soon follows it with a sneak attack).