Me gusta lo dulces que están las uvas este verano.

Because the thing being liked is not just las uvas. It is the whole idea lo dulces que están las uvas este verano = how sweet the grapes are this summer.

In Spanish, when gustar is followed by a whole clause or idea, it usually stays in the singular: gusta.

• Me gustan las uvas = I like grapes.
• Me gusta lo dulces que están las uvas = I like how sweet the grapes are.

So here, gusta agrees with the whole statement, not with uvas.

This is a very common Spanish structure used to express degree or intensity:

lo + adjective + que

Here it means something like:

• how sweet
• the fact that they are so sweet

So:

• lo dulces que están las uvas = how sweet the grapes are

This lo is not the masculine article the. It is a neuter lo, used to turn an adjective phrase into an abstract idea.

Other examples:

• Me sorprende lo rápido que corre. = I am surprised by how fast he runs.
• No imaginas lo difícil que fue. = You cannot imagine how difficult it was.

Because dulces describes las uvas, which is feminine plural.

Adjectives in Spanish agree in number, and sometimes gender, with the noun they describe:

• la uva dulce
• las uvas dulces

Even though the sentence starts with lo, the adjective still agrees with uvas, so it must be dulces.

Spanish often uses estar for conditions or states that are seen as temporary, changeable, or true at a particular moment.

Here, the sentence is talking about how sweet the grapes are this summer, so it is understood as a current condition, not a permanent characteristic of grapes in general.

So:

• las uvas están dulces este verano = the grapes are sweet this summer

If you used son, it would sound more like a general defining quality, which is not the point here.

In this pattern, que links the degree expression to the rest of the clause.

Think of the structure as:

• lo + adjective + que + verb

So:

• lo dulces que están las uvas = how sweet the grapes are

You do not translate que word for word here. It is just part of the fixed Spanish structure.

Because lo dulces que están las uvas is already a complete structure.

It is not built like:

• the sweet thing that...

Instead, it is built like:

• how sweet ... are

So lo dulces que están works as one unit meaning how sweet they are.

This can feel unusual to English speakers because English does not use a direct equivalent of lo + adjective + que.

Spanish often uses time expressions without a preposition when they function adverbially.

So este verano simply means this summer.

Other examples:

• Este año viajo más. = This year I am travelling more.
• Esta semana trabajo desde casa. = This week I am working from home.

You could say en verano to mean in summer / during summer in a general sense, but este verano by itself is perfectly natural for this summer.

No, not in standard Spanish.

It should be lo dulces que están las uvas because dulces agrees with uvas.

• las uvas = plural
• therefore dulces = plural

So the correct sentence is:

Me gusta lo dulces que están las uvas este verano.

Yes, that is a helpful way to understand gustar.

Spanish structures gustar differently from English to like:

• Me gustan las uvas = literally, the grapes please me
• Me gusta lo dulces que están las uvas = literally, how sweet the grapes are pleases me

That is why the indirect object pronoun me appears, and why the verb agrees with what is pleasing, not with the person.

Yes, but the given order is the most natural.

The sentence begins with Me gusta, which is very common in Spanish. It puts the reaction first:

• Me gusta lo dulces que están las uvas este verano.

You could rearrange parts for emphasis, but it would sound less neutral. For example:

• Lo dulces que están las uvas este verano me gusta is possible in theory, but not natural in normal conversation.

So the original order is the best one to learn.

Yes, a little. The structure lo + adjective + que often adds an emotional or evaluative tone.

So this is not just a flat statement about sweetness. It suggests appreciation, almost like:

• I really like how sweet the grapes are this summer
• I like just how sweet the grapes are this summer

It is stronger and more expressive than a simpler sentence like:

• Me gusta que las uvas estén dulces este verano.

That alternative is grammatical, but it does not have exactly the same natural, vivid feel.