После отпуска будничная жизнь кажется мне слишком тихой.

Because после always requires the genitive case.

• отпуск = vacation, leave
• отпуска = genitive singular of отпуск

So:

• после отпуска = after the vacation / after vacation

This is a fixed grammar pattern:

• после работы = after work
• после урока = after the lesson
• после обеда = after lunch

Because будничная is an adjective describing жизнь, and it has to agree with it in gender, number, and case.

Here:

• жизнь is feminine
• жизнь is singular
• жизнь is in the nominative case because it is the subject

So the adjective must also be feminine singular nominative:

• будничный → masculine
• будничная → feminine
• будничное → neuter
• будничные → plural

Будничная жизнь means something like everyday life, routine life, or ordinary day-to-day life. It often has a slightly mundane or non-festive feeling.

The subject is будничная жизнь.

That is why the verb is кажется, which is 3rd person singular:

• жизнь кажется = life seems

Russian verbs agree with the subject. Since жизнь is singular, the verb is singular too.

If the subject were plural, the verb would also be plural:

• будни кажутся мне слишком тихими = weekdays seem too quiet to me

Because with казаться (to seem), the person who experiences the impression is usually put in the dative case.

So:

• мне = to me
• тебе = to you
• ему / ей = to him / her
• нам = to us

In this sentence:

• будничная жизнь кажется мне...
  = everyday life seems to me...

This is a very common pattern in Russian:

• Мне кажется, что... = It seems to me that...
• Этот фильм кажется мне скучным. = This movie seems boring to me.

Because after казаться, the describing word often goes into the instrumental case.

So although жизнь is nominative as the subject, the word describing how it seems is instrumental:

• тихая = nominative feminine singular
• тихой = instrumental feminine singular

Pattern:

• X кажется Y-им / Y-ой = X seems Y

Examples:

• Он кажется уставшим. = He seems tired.
• Она кажется счастливой. = She seems happy.
• Жизнь кажется тихой. = Life seems quiet.

So in your sentence:

• будничная жизнь кажется мне слишком тихой

the form тихой is exactly what we expect after кажется.

Слишком means too in the sense of excessively.

So:

• слишком тихой = too quiet

It suggests that the quietness feels like more than desired or more than feels comfortable, especially after the contrast of a vacation.

Compare:

• очень тихой = very quiet
• слишком тихой = too quiet

So слишком is stronger and more evaluative than очень.

Yes. Russian word order is fairly flexible, although the neutral version here is:

• После отпуска будничная жизнь кажется мне слишком тихой.

That sounds natural and balanced.

You could also say:

• Будничная жизнь после отпуска кажется мне слишком тихой.
• Мне после отпуска будничная жизнь кажется слишком тихой.

These versions are still grammatical, but the emphasis shifts slightly.

Very roughly:

• После отпуска... puts the time frame first
• Будничная жизнь... puts the subject first
• Мне... can emphasize my personal impression

So the original sentence is a normal, natural way to say it.

The dictionary form is казаться, which means to seem / to appear.

This is a standard Russian verb; you usually learn it as a whole item:

• казаться = to seem

The -ся here is not something you should try to translate literally. In many Russian verbs, -ся forms a verb with its own meaning, and казаться is simply the normal verb for seem.

Compare:

• казаться = to seem
• показаться = to seem, to appear briefly, to strike someone as

So it is best to memorize the pattern:

• что-то кажется кому-то каким-то

For example:

• Дом кажется большим. = The house seems big.
• Эта идея кажется мне странной. = This idea seems strange to me.

Yes, and it would sound natural, but the nuance is a little different.

• повседневная жизнь = everyday life, daily life
  This is a more neutral and common expression.
• будничная жизнь = routine life, ordinary non-holiday life
  This often emphasizes the contrast with celebration, vacation, or something special.

In this sentence, будничная жизнь works especially well because the speaker is contrasting normal routine life with отпуск.

So:

• После отпуска повседневная жизнь кажется мне слишком тихой.
  = natural
• После отпуска будничная жизнь кажется мне слишком тихой.
  = also natural, with a stronger sense of back to ordinary routine

Yes. Тихий literally means quiet, but in Russian it can describe not only sound level, but also a general feeling of calmness, slowness, or lack of activity.

So here слишком тихой probably does not only mean not noisy enough. It can also suggest:

• too calm
• too uneventful
• too still
• lacking excitement after vacation

That is why the sentence feels natural: after an active or emotional holiday, ordinary life may feel too quiet in a broader sense.

The stresses are:

• послЕ
• отпУска
• буднИчная
• жИзнь
• кАжется
• мнЕ
• слИшком
• тИхой

So the whole sentence is pronounced roughly as:

ПослЕ отпУска буднИчная жИзнь кАжется мнЕ слИшком тИхой.

Stress is important in Russian, so it is good to learn words together with their stress from the start.