Это пирожное слишком сладкое, зато моя сестра его обожает.

Here это means this: this pastry / this cake.

It matches пирожное, which is:

• neuter
• singular
• nominative

So это пирожное = this pastry.

A useful point: это can also mean something like this/it is in other sentence types, but here it is simply the demonstrative word modifying пирожное.

Пирожное usually means a small sweet pastry, cake, or individual dessert—something like a pastry-shop item.

It does not mean a full-sized cake in the general sense. For comparison:

• торт = cake
• пирог = pie / baked filled dish
• пирожок = small pie / turnover
• пирожное = pastry / small cake / dessert item

It is also a neuter noun, which matters for agreement in the sentence.

Because it agrees with пирожное.

In Russian, adjectives must agree with the noun in:

• gender
• number
• case

Here пирожное is:

• neuter
• singular
• nominative

So the adjective also has to be neuter singular nominative:

• сладкий = sweet (dictionary form, masculine)
• сладкая = feminine
• сладкое = neuter
• сладкие = plural

So пирожное сладкое literally means the pastry is sweet / sweet pastry.

Because in Russian, the verb to be is usually omitted in the present tense.

So Russian says:

• Это пирожное слишком сладкое. literally: This pastry too sweet.

But in natural English we translate it as:

• This pastry is too sweet.

In past or future tense, forms of быть appear:

• Это пирожное было слишком сладким. = This pastry was too sweet.
• Это пирожное будет слишком сладким. = This pastry will be too sweet.

Слишком means too, in the sense of excessively.

So:

• слишком сладкое = too sweet

This is different from very sweet:

• очень сладкое = very sweet
• слишком сладкое = too sweet

So слишком usually implies that the amount is more than desired.

Зато is a very useful word. It means something like:

• but
• but on the other hand
• however, as a compensating point
• the good thing is that...

In this sentence:

• Это пирожное слишком сладкое, зато моя сестра его обожает.

The idea is: It’s too sweet, but at least my sister loves it.

Why not just но?

• но = plain but
• зато = but this positive thing makes up for it

So зато often introduces a contrast where the second part balances or compensates for the first part.

Его refers back to пирожное and means it.

It is the direct object of обожает (adores/loves), so Russian uses the accusative.

For the pronoun он / оно, the accusative form is:

• его

So:

• моя сестра его обожает = my sister adores it

Even though пирожное is neuter, the object pronoun is still его.

A quick comparison:

• Он любит торт. = He likes the cake.
• Он любит его. = He likes it.

Both are possible, but the word order changes the feel a little.

Russian word order is flexible, and pronouns often appear before the verb, especially when they are unstressed and already known from context.

So:

• моя сестра его обожает sounds very natural
• моя сестра обожает его is also possible, but may give a bit more emphasis to его

In this sentence, его is just the known object (the pastry), so placing it before the verb is quite normal.

Обожает comes from обожать, which means:

• to adore
• to absolutely love

So it is stronger than plain любить in many contexts.

Here:

• моя сестра его обожает = my sister adores it / absolutely loves it

Grammatically, обожает is:

• 3rd person singular
• present tense

from обожать:

• я обожаю
• ты обожаешь
• он / она обожает

Because моя сестра is the subject of the second clause.

In:

• зато моя сестра его обожает

the person doing the action is my sister, so Russian uses the nominative:

• моя сестра = my sister

Then the thing receiving the action is его = it, the direct object.

So the structure is:

• моя сестра = subject
• его = object
• обожает = verb

Because they are both neuter singular nominative forms, but they belong to different word types:

• пирожное = noun
• сладкое = adjective

Russian neuter singular nominative often ends in:

• -ое
• -ее

So it is normal for a neuter noun and a matching adjective to look similar in form.

Compare:

• холодное молоко = cold milk
• вкусное яблоко = tasty apple
• сладкое пирожное = sweet pastry

This similarity is a sign of grammatical agreement, not a coincidence.

Sometimes Russian can omit an understood object in conversation, but here keeping его is the most natural and complete version.

So:

• моя сестра его обожает = natural and clear

If you said only:

• моя сестра обожает

it would usually sound incomplete, because обожать normally needs an object: adore what?

So repeating the object as его is exactly what Russian normally does here.

Yes, it sounds natural.

It has a very typical structure:

1. a negative or critical comment
2. then зато introduces a balancing positive point

So the sentence feels idiomatic:

• Это пирожное слишком сладкое, зато моя сестра его обожает.

A native speaker would understand it as something like:

• This pastry is too sweet, but my sister loves it, so that’s one good thing.