La primera escultura me impresionó más que el retrato del fondo.

Me is the indirect object pronoun meaning to me in this sentence.

• impresionar = to impress
• me impresionó = it impressed me

Spanish usually puts these object pronouns before a conjugated verb:

• Me impresionó = It impressed me
• Te impresionó = It impressed you
• Nos impresionó = It impressed us

So La primera escultura me impresionó literally means The first sculpture impressed me.

Impresionó is the preterite, which presents the impression as a completed event: at that moment, the sculpture impressed the speaker.

• me impresionó = it impressed me / I was impressed by it
• me impresionaba = it was impressing me / it used to impress me / it struck me as impressive

In a sentence about a specific reaction to seeing something, the preterite is the most natural choice:

• La primera escultura me impresionó más...
  = The first sculpture impressed me more...

If you used impresionaba, it would sound more ongoing, habitual, or descriptive.

Más que means more than.

In this sentence:

• La primera escultura me impresionó más que el retrato del fondo.

the idea is:

• The first sculpture impressed me more than the portrait in the background / at the back did.

This is the normal way to compare two things in Spanish:

• más que = more than
• menos que = less than
• tan ... como = as ... as

Examples:

• Me gustó más que la otra. = I liked it more than the other one.
• Era más grande que el cuadro. = It was bigger than the painting.

Because Spanish often leaves out repeated words when they are already understood.

The full version would be:

• La primera escultura me impresionó más que el retrato del fondo me impresionó.

But that sounds repetitive, so Spanish normally omits the repeated part:

• La primera escultura me impresionó más que el retrato del fondo.

English does the same:

• The first sculpture impressed me more than the portrait in the back.

The missing idea is understood as impressed me.

In most normal contexts, la primera escultura means the first sculpture in some sequence:

• the first one you saw
• the first one mentioned
• the first one in a series

It does not usually mean the main sculpture or the best sculpture.

If you wanted the main or principal one, Spanish would more naturally use words like:

• la escultura principal
• la escultura más importante

So here primera is most naturally understood as first.

Del fondo is a contraction of de + el:

• de el → del

El retrato del fondo means something like:

• the portrait at the back
• the portrait in the background
• the portrait in the back of the room/gallery

The exact nuance depends on context.

For example:

• In a museum room, del fondo often means at the back.
• In a picture or visual scene, it can mean in the background.

So el retrato del fondo identifies which portrait we mean: the one located farther back.

Because in standard Spanish, de + el normally contracts to del.

• de el fondo ❌
• del fondo ✅

This contraction happens with de + el and a + el:

• de + el = del
• a + el = al

Examples:

• la puerta del museo = the museum’s door / the door of the museum
• voy al centro = I’m going to the centre

One important exception: If El is part of a proper name, you do not contract it.

• de El Escorial ✅
• not del Escorial in that case if the official name is El Escorial

But here el fondo is not a proper name, so del fondo is required.

Because adjectives in Spanish usually agree with the noun they describe in gender and number.

• escultura is feminine singular
• so the adjective must also be feminine singular: primera

Compare:

• el primer cuadro = the first painting
• la primera escultura = the first sculpture
• los primeros cuadros = the first paintings
• las primeras esculturas = the first sculptures

Also notice that primero becomes primer before a masculine singular noun:

• el primer retrato
• but la primera escultura

Yes, grammatically you could, but the meaning changes.

• La primera escultura me impresionó más que el retrato del fondo.
  = The first sculpture impressed me more than the portrait did.

• La primera escultura impresionó más que el retrato del fondo.
  = The first sculpture impressed more than the portrait in the back did.

Without me, the sentence becomes less personal and more incomplete unless the context makes clear whom or what it impressed. In most situations, me is needed because the sentence is about the speaker’s reaction.

Not always.

Impresionar usually means to make a strong impression on someone, and that can be positive, negative, or simply powerful.

Examples:

• Me impresionó su talento. = His/Her talent impressed me.
  (positive)
• Me impresionó la violencia de la escena. = The violence of the scene shocked/struck me.
  (negative or disturbing)
• La escultura me impresionó. = The sculpture made a strong impression on me.
  (neutral to positive depending on context)

So in your sentence, it probably means the first sculpture had a stronger effect on the speaker, but not necessarily in a purely positive way.

You can add a mí for emphasis:

• La primera escultura me impresionó más que el retrato del fondo, a mí.
• more naturally: A mí, la primera escultura me impresionó más que el retrato del fondo.

This adds contrast or emphasis, for example if someone else had a different reaction.

Spanish often uses both:

• A mí = the stressed form
• me = the required pronoun in the sentence

So:

• A mí me impresionó más la primera escultura.
  = Me, I was more impressed by the first sculpture.

Retrato usually means portrait, but in context it often refers to a portrait painting, portrait photograph, or even a portrait in another medium.

So:

• el retrato del fondo = the portrait at the back / in the background

If you need to be more specific, Spanish can say:

• retrato al óleo = oil portrait
• retrato fotográfico = photographic portrait
• cuadro = painting
• pintura = painting

But on its own, retrato is perfectly natural if the important idea is simply that it is a portrait.

The structure is:

• [Subject] + me + [verb] + más que + [other thing]

So literally:

• La primera escultura = The first sculpture
• me impresionó = impressed me
• más que = more than
• el retrato del fondo = the portrait at the back / in the background

A very natural English rendering is:

• The first sculpture impressed me more than the portrait at the back.

Or, if you want the comparison to be extra explicit:

• The first sculpture impressed me more than the portrait at the back did.

That final did is often omitted in both languages when the meaning is already clear.