This is indeed a very funny Spanish comedy, with good acting by all the leads, a solid script boasting plenty of amusing situations and dialogues that never become too over- the-top or superficial, and some beautiful shots of both País Vasco (Basque Country) and Andalucía (Andalusia).
A word of warning, though: This film plays with local accents and stereotypes, current and past Spanish politics, and memes that you will have to be familiar with ahead of time to understand the gags. It is also heavily reliant on how Spaniards envision Basques, thus limiting its comedic effect to Spanish audiences (or at the very least, people familiar with the aforementioned themes).
I, being a Spaniard, had no problem having fun with this film. As enjoyable as it was, however, I can't help but find it undeserving of being the most successful film at the Spanish Box Office of all time, considering all the great cinema and the superior films this country has created in the past. But perhaps it's not so much the quality but the timing of this film that has led to its success: This film makes you laugh and sends a message of unity and love despite our differences. This may just be what Spaniards need in such hard times.