, yes, a good villain should be intelligent. I mean, you can still have a dumb villain, like Maul was, but you don't really hate him. I have to admit that part of me felt sympathy for Maul because it seemed like he was so naive that he didn't realize he was being taken advantage of.
Smarter villains, while not necessarily strong, are more dangerous, in my opinion. Darth Vader, the Emperor, and Grand Admiral Thrawn - all were intelligent, some of them frighteningly so.
Vader, he seemed more coniving with a good dose of brute strength to go along with his prowess in the Force. Not necessarily a genius, but definitely not one of the dull tools in the shed either.
The Emperor, he was a highly intelligent, and incredibly strong with the Force. That, combined with his unlimited arrogance made him one of my favorite villains of all time. But as we all know, his over-confidence was also the weakness that helped bring about his downfall.
Grand Admiral Thrawn is by far the last person I want to face in a space battle. An enemy finding out they were facing Thrawn would likely demoralize their entire force. Again, though, he knew he was a genius and this created a false sense of safety for him. I found it very interesting that he relished the surprise of the Nogrhi assasin that killed him - he admired the fact that he had been outsmarted, and this made me like him as a villain even more.
I guess to summarize, in my opinion, a villain has to have some aspect about them that makes them seem dangerous. It can be brute strength, power, intelligence, experience, history, etc. I think a villain is more interesting when he/she is a combination of the above, and when there personality of that villain is fleshed out in exquisite detail