Learn Hardcore Croatian: Taj film je dosadan, ali je razgovor poslije filma bio zanimljiv. - That movie is boring, but the conversation after the movie was interesting.

Taj film je dosadan = That film is boring (the specific one we both know which one).
Film je dosadan = The film / A film is boring (more general, or it’s clear from context which film, but you’re not pointing it out so explicitly).

Croatian has a three-way distinction:

ovaj film – this film (near the speaker)
taj film – that film (near the listener or just mentioned)
onaj film – that film over there / that one (far away, or more distant in context)

In this sentence, taj shows you are talking about a specific, already identified movie.

Why is it je dosadan for the film but bio zanimljiv for the conversation? Why different tenses?

je dosadan = is boring (present tense of biti – to be)
bio zanimljiv = was interesting (past tense of biti
- adjective)

The sentence implies:

The film (as a work) is boring in general or is being judged now: That film is (in general) boring.
The conversation happened in the past (after watching that particular film): the conversation after the film was interesting (at that time).

So the different tenses reflect a general evaluation of the film vs. a one-time event that happened in the past.

Why is it dosadan and zanimljiv, not dosadno or zanimljivo?

Dosadan and zanimljiv are adjectives that must agree with the noun film and razgovor, which are both:

masculine
singular
in the nominative case (they are the subjects)

Masculine singular nominative adjectives usually end in -an, -en, -iv, -ljiv, etc.:

dosadan film – a boring film
zanimljiv razgovor – an interesting conversation

Forms like dosadno, zanimljivo are neuter singular and would match neuter nouns (e.g. dijete je dosadno – the child is boring; to je zanimljivo – that is interesting), not film/razgovor.

What case is filma in poslije filma, and why is it not just poslije film?

Filma is in the genitive singular case.

The preposition poslije (after) always takes the genitive:

poslije filma – after the film
poslije posla – after work
poslije ručka – after lunch

So you must change film (nominative) to its genitive form filma after poslije. Saying poslije film would be ungrammatical in standard Croatian.

Can I use nakon or posle instead of poslije? Do they mean the same thing?

Yes, with small regional and stylistic differences:

poslije filma – after the film (common and standard in Croatia and Bosnia)
nakon filma – after the film (also standard, a bit more neutral/formal, used everywhere)
posle filma – after the film (more typical for Serbian; in Croatia you’ll mainly see poslije)

All three take the genitive (filma) and mean essentially the same thing in everyday use: after the film.

Why does je appear before razgovor in ali je razgovor poslije filma bio zanimljiv? Could it be ali razgovor poslije filma je bio zanimljiv?

Je is the 3rd person singular present of biti (to be) and it is a clitic (an unstressed short word). Croatian clitics usually like to appear very early in the clause, often in “second position”.

Both of these are possible:

… ali je razgovor poslije filma bio zanimljiv.
… ali razgovor poslije filma je bio zanimljiv.

The first version (with je right after ali) is very common and sounds completely natural. The second version (with je after razgovor poslije filma) is also grammatical; it just places the clitic slightly later in the clause and can feel a bit more marked or emphatic in some contexts.

What you cannot do is put je at the very end:
✗ … ali razgovor poslije filma bio zanimljiv je. – incorrect.

Can the word order inside the second part be changed more? For example: ali razgovor nakon filma bio je zanimljiv?

Yes, some variation is allowed due to relatively flexible word order:

All of these are grammatical and natural:

…, ali je razgovor poslije filma bio zanimljiv.
…, ali razgovor poslije filma je bio zanimljiv.
…, ali razgovor poslije filma bio je zanimljiv.

Moving je before or after bio (je bio vs bio je) does not change the basic meaning; it can affect rhythm or emphasis slightly, but all three are fine in normal speech and writing. The key is: je must appear once in that clause and must not be moved to the very end.

Could I drop the second je and say … ali razgovor poslije filma bio zanimljiv?

In standard Croatian, no: you need the auxiliary je to form the past tense with bio for 3rd person singular:

razgovor je bio zanimljiv – correct
razgovor bio zanimljiv – incorrect in standard language

You might occasionally hear auxiliary verbs dropped in very casual speech, but learners should treat that as non-standard or elliptical. For correct grammar, include je in the second clause.

Is the comma before ali necessary, like the comma before but in English?

Yes. In Croatian, when ali (but) connects two independent clauses, you normally put a comma before it:

Taj film je dosadan, ali je razgovor poslije filma bio zanimljiv.

This is parallel to English:
That film is boring, but the conversation after the film was interesting.

You usually do not use a comma when ali connects just words or short phrases, not full clauses:

Film je dosadan ali kratak. – The film is boring but short. (often written without a comma)

Could the sentence start with the conversation instead of the film? For example: Razgovor poslije filma je bio zanimljiv, ali je taj film dosadan.

Yes, that is perfectly grammatical and natural:

Razgovor poslije filma je bio zanimljiv, ali je taj film dosadan.

This version simply changes the focus: it starts with the positive part (interesting conversation) and then contrasts it with the negative judgment of the film. Word order in Croatian is flexible enough to allow this kind of reordering without changing the basic meaning.