Uuno looks like he's been pulled trough a car engine while it's still running. Despite the hideous result, Uuno seems to be a real player when it comes to woman so one essential "subplot" in most of the Uuno movies as in this one also, is Uuno picking up ladies while his wife's nagging at him. Second "subplot" in all the Uuno movies I remember, is his eternal battle with his father-in-law Tuura who ranks high in politics. Uuno gives him hard time and somehow seems to get him constantly into troublesome situations.
Ere Kokkonen relies heavily on Loiri's actor skills and outlook of the character since he himself has no talent as a director or as a writer. The characters are unimaginative and the comedy is really weak. Most of the shots have perhaps been shot only once and then forgotten. Soundtrack consists of pretty weird eighties synth sounds which are perhaps the funniest part in the movies although used in helpful manner to pinpoint the scenes to laugh at (so you wouldn't forget to). For example to highlight some autistic look on Uuno's face or when Tuura finds out that he has to suffer because of something that Uuno did. The whole "plot" is ridiculous and worth while mentioning only briefly: As the title suggests, Uuno goes to Spain with his wife and her parents. Then the subplots start to loop. Uuno gives hard time to Tuura, chases womens etc. Uunos mechanic buddies from Finland are also included in this film so that the audience wouldn't feel alienated from the previous movies at all.
I think there is no one Uuno movie that surpasses the others as being the ultimate failure, all of them are pretty standard ultra low quality and this one is no exception. If you have seen one, you have seen them all. All that changes is the surroundings where the comedy is supposed to happen. Hopefully Uuno is at least for now dead and buried.