Мне кажется, что сценарий этого мюзикла сложнее, чем сценарий вчерашнего фильма.

Мне кажется literally means it seems to me. In many contexts, it works like a softer I think.

So:

• я думаю = I think / I am thinking
• мне кажется = it seems to me

In this sentence, мне кажется makes the statement sound a little less direct and a little more subjective.

Also, Russian often prefers this structure where English would simply say I think.

Because the expression is built as to me it seems, not I seem.

• мне is the dative case of я
• the dative here marks the person who experiences the impression

So:

• я = I
• мне = to me

That is why мне кажется means it seems to me.

Что is the conjunction that.

So the sentence structure is:

• Мне кажется, что ...
• It seems to me that ...

Yes, in everyday Russian, что is often omitted:

• Мне кажется, сценарий этого мюзикла сложнее...

That sounds natural in speech. Including что is also completely normal and can sound slightly more explicit or more written.

Because they depend on the noun сценарий and mean the script of ...

Russian often uses the genitive where English uses of.

So:

• сценарий этого мюзикла = the script of this musical
• сценарий вчерашнего фильма = the script of yesterday’s film

This is a very common pattern:

• дом брата = the brother’s house / the house of the brother
• конец фильма = the end of the film

Because adjectives and adjective-like words in Russian must agree with the noun they describe in:

• gender
• number
• case

Here:

• мюзикла is masculine singular genitive
• фильма is masculine singular genitive

So the modifiers must also be masculine singular genitive:

• этот → этого
• вчерашний → вчерашнего

This is standard adjective agreement.

Сложнее is the comparative form of сложный:

• сложный = complex
• сложнее = more complex

Yes, Russian can also form comparisons with более:

• более сложный

But in this sentence, сложнее is the more natural and compact choice.

Compare:

• Сценарий сложнее = The script is more complex
• Сценарий более сложный = also possible, but less simple/direct here

A useful point: сложнее does not change for gender, number, or case.

Чем means than in comparisons.

So:

• сложнее, чем сценарий вчерашнего фильма
• more complex than the script of yesterday’s film

After чем, Russian can give:

• a full clause
• or just the phrase being compared

Here, the full idea is something like:

• ...сложнее, чем сценарий вчерашнего фильма [сложен / является сложным]

But Russian normally leaves the repeated part unstated.

It is repeated for clarity:

• сценарий этого мюзикла сложнее, чем сценарий вчерашнего фильма

This clearly compares one script with another script.

You usually should not just remove сценарий and say:

• ...чем вчерашнего фильма

That sounds wrong.

Russian does allow other ways to avoid repetition, but they are different structures, for example:

• ...сложнее сценария вчерашнего фильма

So in the exact чем structure, repeating сценарий is the safe and natural choice.

Yes. Russian often allows a comparative followed directly by the genitive:

• сценарий этого мюзикла сложнее сценария вчерашнего фильма

This means the same thing.

Very roughly:

• сложнее, чем ... = more explicit than ...
• сложнее + genitive = a more compact comparison

Both are grammatical. The version with чем is often clearer for learners.

Because Russian has no articles like a or the.

Russian shows definiteness through:

• context
• word order
• demonstratives such as этот / эта / это

So:

• сценарий can mean a script or the script, depending on context
• этого мюзикла helps specify of this musical

English needs articles; Russian does not.

Yes. Мюзикл is a loanword, but in modern Russian it declines like a regular masculine noun.

For example:

• nominative: мюзикл
• genitive: мюзикла
• dative: мюзиклу
• instrumental: мюзиклом
• prepositional: о мюзикле

So этого мюзикла is completely regular.

Yes, Russian word order is flexible, though the neutral order here is very natural.

Original:

• Мне кажется, что сценарий этого мюзикла сложнее, чем сценарий вчерашнего фильма.

You could also say:

• Сценарий этого мюзикла, мне кажется, сложнее, чем сценарий вчерашнего фильма.

That version emphasizes сценарий этого мюзикла a bit more.

Because Russian marks relationships mostly through case endings, word order is often used for emphasis rather than basic grammar.

Not usually. In this context, сценарий means:

• script
• screenplay

That is the normal word for the script of a film, show, or musical.

English scenario is often something like a possible situation or set of circumstances, and that is not the main meaning here. So learners should be careful with this false friend.