El Dorado is a good film, but John Wayne made many better films. His best film (let alone Western) is easily The Searchers, IMHO. It's got John Ford's signature use of the natural environment as more than just a pretty backdrop. But it also has John Wayne's absolute best performance of all time (I have no clue why he wasn't nominated for an Academy Award for his performance.) If you haven't seen it, I highly recommend you watch The Searchers.El Dorado--happens to be my favorite of the John Wayne movies.
Another John Wayne film I highly recommend is The Shootist, his last film. It's another Oscar-worthy performance. He really left everything on the field with that last performance. The film also felt very much like a swan song, not just for John Wayne, but for the Westerns and other action films he helped popularize. That's not to say no one ever made Westerns or action films after John Wayne retired, rather, the Wayne-style of films was no more.