Learn Hardcore French: Ce film est intéressant au début, mais la fin est vraiment ennuyeuse. - This movie is interesting at the beginning, but the ending is really boring.

ce = this/that (masculine singular, before a consonant): ce film
cet = this/that (masculine singular, before a vowel or mute h): cet homme, cet arbre
cette = this/that (feminine singular): cette histoire
ces = these/those (plural, any gender): ces films, ces histoires

Because film is masculine, singular, and starts with a consonant sound, you must use ce → Ce film.

How do I know that film is masculine?

Unfortunately, grammatical gender in French often has to be memorized. There are some patterns, but many exceptions.

In practice:

Look words up in a dictionary. You’ll see (n.m.) for nom masculin or (n.f.) for nom féminin.
When you learn a noun, learn it with its article: un film, le film (masculine); une histoire, la histoire → actually l’histoire (feminine).

So you memorize un film / le film and that tells you the gender.

Why is it Ce film est intéressant and not C’est intéressant?

You can say both, but they don’t mean exactly the same:

Ce film est intéressant = This film is interesting.
You’re talking specifically about this particular film.
C’est intéressant = That’s interesting.
This is more general and could refer to a situation, an idea, or something just mentioned, not necessarily the film as a concrete object.

In your sentence, you want to talk directly about the film as a thing, so Ce film est intéressant is the most precise.

Why is intéressant placed after film? Can it go before the noun?

Most French adjectives come after the noun:

un film intéressant
une histoire compliquée

Some very common, short adjectives go before the noun (often called BANGS: beauty, age, number, goodness, size), such as beau, vieux, bon, petit.

Intéressant normally goes after the noun. Putting it before (un intéressant film) sounds poetic or very marked, not natural in everyday speech. So:

Natural: Ce film est intéressant.
Marked/odd in normal speech: Ce intéressant film.

What exactly is au début grammatically? Why not à le début?

Au is a contraction:

à + le = au

So au début literally comes from à le début (at the beginning), but in correct French you must contract à le → au.

That’s why you say:

au début (at the beginning)
au cinéma (at the cinema)
au film (to the film / in the film, in some contexts)

You only use plain à before feminine nouns (à la maison) or plural nouns (aux États-Unis from à + les).

Is there a difference between au début and au commencement?

Both can mean at the beginning, but:

au début is much more common and neutral in everyday speech.
au commencement can sound more formal, literary, or solemn, and is used less in casual conversation.

For talking about a film, au début is the natural choice:

Ce film est intéressant au début…
sounds completely ordinary and idiomatic.

Why does it say la fin and not la fin du film?

French, like English, often drops the obvious part when the context is clear.

Ce film est intéressant au début, mais la fin est vraiment ennuyeuse.
We already know we’re talking about the film, so la fin is understood as la fin du film.

If you want to be more explicit, you can say:

…mais la fin du film est vraiment ennuyeuse.

Both are correct; the shorter version is just more natural once the context is established.

Why is it ennuyeuse and not ennuyeux or ennuyant?

This is about agreement and word choice:

Agreement:
- la fin is feminine singular.
- The adjective must agree: feminine singular of ennuyeux is ennuyeuse.
- So: la fin est ennuyeuse.
Masculine examples:
- Ce film est ennuyeux. (masculine singular)
- Ces films sont ennuyeux. (masculine plural)
Ennuyeux / ennuyeuse vs ennuyant / ennuyante:
- ennuyeux / ennuyeuse is the standard, common adjective for boring.
- ennuyant / ennuyante also exists, but many speakers use it less often or with a more “causing annoyance” nuance. In everyday French, ennuyeux / ennuyeuse is the safest choice for boring.

So la fin est vraiment ennuyeuse is the most natural here.

Could I say Ce film est intéressant au début, mais la fin est vraiment ennuyeux?

No, that would be grammatically wrong, because of agreement.

la fin is feminine singular, so the adjective must be feminine singular too:
- ennuyeuse ✅
- ennuyeux ❌ (masculine singular / masculine plural form)

Correct options:

…mais la fin est vraiment ennuyeuse. ✅
…mais ce film est vraiment ennuyeux à la fin. ✅ (if you change the structure and refer back to film, which is masculine)

What does vraiment add here, and where can I put it in the sentence?

Vraiment means really / truly / very. It intensifies the adjective:

ennuyeuse = boring
vraiment ennuyeuse = really boring / very boring

The most natural placement is right before the adjective:

la fin est vraiment ennuyeuse.

Other possibilities:

la fin est ennuyeuse, vraiment. (more spoken, like an afterthought, a bit emphatic)
la fin est ennuyeuse, mais vraiment. (very colloquial, adds emotional emphasis)

In careful standard usage, keep vraiment just before ennuyeuse as in the original sentence.

Could I say mais la fin est super ennuyeuse or mais la fin est très ennuyeuse instead of vraiment ennuyeuse?

Yes, both are possible, with slightly different tones:

très ennuyeuse = very boring
Neutral, standard intensifier.
super ennuyeuse = really/so boring
Very informal/colloquial, common in spoken French, especially among younger speakers.
vraiment ennuyeuse = really boring / genuinely boring
Neutral and idiomatic in both spoken and written French.

So you can say:

…mais la fin est très ennuyeuse. (neutral)
…mais la fin est vraiment ennuyeuse. (neutral)
…mais la fin est super ennuyeuse. (informal)

What’s the difference between la fin est vraiment ennuyeuse and la fin est vraiment nulle?

Both criticize the ending, but the nuance is different:

ennuyeuse = boring, dull
You’re focusing on the lack of interest / slow pace.
nulle (from nul/nulle) = really bad, lame, awful (informal)
You’re judging the quality more strongly; it sounds harsher and more colloquial.

Examples:

La fin est vraiment ennuyeuse.
= The ending is really boring; nothing happens, it drags.
La fin est vraiment nulle.
= The ending is really terrible; maybe badly written, disappointing, or stupid.

Both are fine; it just depends on what exactly you want to express and how strong you want the criticism to be.

Is there any liaison or tricky pronunciation in Ce film est intéressant au début, mais la fin est vraiment ennuyeuse?

A few points:

Ce film:
film ends with a consonant cluster lm. In careful pronunciation you keep both consonants: [film], but the final m is not strongly released in fast speech.
est intéressant:
There is a liaison: est‿intéressant → pronounce the t linking: [ɛ tɛ̃teʁesɑ̃].
au début:
The t of au is silent (there is no t), it’s just [o].
ennuyeuse:
Pronounced roughly [ɑ̃nɥijøz]:
- ennu- gives a nasal vowel at the start.
- -yeu- sounds like the French eu in deux.
- Final -se → pronounced z.

There are several silent letters, but they mainly affect spelling, not the rhythm of the sentence.