Теперь я понимаю, почему многие любят и оперу, и балет: после такого вечера трудно не захотеть прийти на следующую премьеру.

Both can mean now, but they are not always interchangeable.

• теперь often means now, from this point on, as a result of what I’ve learned/experienced
• сейчас often means right now, at this moment

So Теперь я понимаю means something like Now I understand in the sense of I didn’t before, but I do now. That fits the sentence very well.

Многие means many people here.

In Russian, adjectives and pronoun-like words can sometimes stand on their own without an explicit noun if the noun is obvious from context.

So:

• многие любят... = many people love...

You do not need to add люди. In fact, многие люди is possible, but многие alone sounds very natural.

The pattern и X, и Y means both X and Y.

So:

• любят и оперу, и балет = love both opera and ballet

If you said just оперу и балет, that would still be grammatical and natural, but и..., и... gives extra emphasis to the idea of liking both.

They are in the accusative case because they are the direct objects of любят.

The verb любить takes the accusative:

• любить оперу
• любить балет

About the forms:

• опера → оперу in the accusative singular
• балет stays балет in the accusative singular because it is an inanimate masculine noun, and for such nouns the accusative usually looks like the nominative

So the different-looking forms come from noun gender and declension patterns.

The preposition после always requires the genitive case.

So:

• после вечера = after the evening
• после такого вечера = after such an evening

Here:

• вечер → вечера in the genitive singular
• такой → такого to match вечера in gender, number, and case

This is a very common Russian pattern: preposition + required case.

Такого means such a or that kind of.

In после такого вечера, it adds emotion and evaluation:

• not just after an evening
• but after such an evening, meaning an evening so impressive or memorable that the reaction in the second half of the sentence is natural

It agrees with вечера in case, number, and gender.

This is a very common impersonal construction in Russian.

• трудно + infinitive = it is hard/difficult to...

So:

• трудно понять = it is hard to understand
• трудно поверить = it is hard to believe
• трудно не захотеть = it is hard not to want

Russian often omits a formal subject equivalent to English it in such sentences.

It is not a meaningless double negative. It expresses a real idea:

• трудно захотеть = it is hard to want
• трудно не захотеть = it is hard not to want

In other words, the experience is so good that you almost inevitably want to come again.

This type of structure is very common in both Russian and English:

• It’s hard not to smile
• It’s hard not to admire it
• Трудно не улыбнуться
• Трудно не восхититься

Захотеть is the perfective partner of хотеть and often means to come to want, to feel the desire, or to start wanting.

That works well here because the sentence is about the reaction that arises after the evening:

• не захотеть прийти = not to end up wanting to come

If you used не хотеть, it would sound more like a continuing state, while не захотеть focuses on the moment or result of that desire appearing.

So трудно не захотеть is very natural here.

Because прийти is perfective, and it refers to a single completed act of coming.

Here the idea is:

• to come to the next premiere once, on that future occasion

Compare:

• прийти = to come / to arrive once, as a complete event
• приходить = to come regularly / to be coming / to come in general, depending on context

Since the sentence is about feeling motivated to attend a specific future event, прийти is the better choice.

The preposition на is commonly used when talking about going to an event:

• на концерт = to a concert
• на спектакль = to a performance
• на премьеру = to a premiere

When на expresses direction toward an event or place, it usually takes the accusative case.

So:

• следующая премьера → на следующую премьеру

Here:

• следующую is the accusative singular feminine form
• премьеру is also accusative singular feminine

Usually, yes, but with a small usage note.

In Russian, премьера normally means the first performance of a new opera, ballet, play, film, and so on. In this sentence, it most naturally means the next premiere performance at the theater.

So прийти на следующую премьеру suggests wanting to attend the next big new production.

The colon introduces an explanation of the first part.

The structure is:

• Теперь я понимаю, почему... = statement
• после такого вечера трудно... = explanation of that statement

So the colon here works like namely, because, or the reason is that.

It connects the idea very neatly: the speaker now understands why many people love both opera and ballet, and the reason is that after an evening like this, it is hard not to want to come back.