You should, no, you must buy TES III + IV + V. That will be an experience you certainly won't regret. Even Morrowind is still an amazing game, even though it was released more than 10 years ago.
Morrowind is really a good game. Its far better then Oblivion if you take to consideration the time difference. And like always The Witcher is a game you must paly. Especially that a third game with Geralt will be released in around half year from now.