Learn Finnish: Juhla oli ihan kiva. - The party was completely nice.

You start with the negative verb for 'it' (ei) and add the question particle -kö to get Eikö. Then, change the main verb oli to its past tense negative form, ollut. The full question becomes: Eikö juhla ollut ihan kiva?

Does ihan kiva actually mean 'completely nice'?

Literally yes, since ihan means 'completely' or 'quite'. However, in everyday Finnish, ihan kiva usually means 'pretty nice' or 'okay'. It is a very common, slightly toned-down way to say you enjoyed something without sounding overly enthusiastic.

Why is the adjective kiva in its basic form instead of the partitive case?

Because juhla (party) is a singular, countable noun. When describing a whole, countable thing with the verb olla (to be), the adjective stays in the basic nominative form. If you were describing an uncountable mass noun like ruoka (food), you would use the partitive: Ruoka oli kivaa.

Is juhla the best word for a casual weekend party?

Juhla usually implies a slightly more formal celebration or festival, like a wedding or a graduation party. If you are talking about a casual party with friends, Finns usually use the plural spoken-language word bileet.