It is hard to give any general information on the exams in Spanish universites because everything is possible. I had extreme multiple-choice exams with 30 questions for 40 minutes and an answer sheet that was similar to what is used at a driving test. The good side was that it allowed a very fast correction - the bad side, that you better don't mix up the rows. But I also had rather normal open-question exams.
The difficulty of these exams highly depends on the university. Wheras at La Politécnica the exams are extremely hard and can be repeated as often as necessary (6 times is quite a common number of tries) and so Erasmus students do get easier versions, the exams at UC3M have been quite fair and in general more practice-oriented than most TUM exams. Apart from La Politécnica is is normal that an exam can only be repeated 3 times - also similar to Germany.