Takva me komplikacija još uvijek iznenađuje.

Because me is the accusative form of ja (I / me).

In Takva me komplikacija još uvijek iznenađuje, the verb iznenađuje means surprises, so the person experiencing the surprise is the direct object:

• ja = I (nominative, subject form)
• me = me (accusative, object form)

So Croatian structures this like:

• komplikacija iznenađuje me
• literally: the complication surprises me

That is why me is required, not ja.

Takva means such, that kind of, or this sort of, depending on context.

It comes from the pronoun/adjective takav and changes form to agree with the noun it describes. Since komplikacija is feminine singular, the form is:

• masculine: takav
• feminine: takva
• neuter: takvo

So:

• takva komplikacija = such a complication / that kind of complication

It adds a sense like a complication of that sort rather than just a complication.

Because komplikacija is the subject of the sentence, so it stays in the nominative case.

The structure is:

• Takva komplikacija = the subject
• me = the object
• iznenađuje = the verb

So the sentence works like:

• Such a complication surprises me

If komplikacija were the object of another verb, then you might see komplikaciju, but not here.

Because the subject is takva komplikacija, which is singular.

Croatian verbs agree with the subject in person and number. Here the subject is:

• komplikacija = complication (singular)

So the verb must also be singular:

• iznenađuje = surprises / is surprising

Even though me refers to I, that does not control the verb. The subject does.

Još uvijek means still.

Both words together are very common and natural in Croatian when you want to emphasize continuing persistence:

• još uvijek = still

You will also often hear just još used to mean still, especially in speech:

• Takva me komplikacija još iznenađuje.

That is also correct.
Using još uvijek can sound a bit fuller or more explicit.

Yes, Croatian word order is flexible, although some orders sound more natural depending on emphasis.

The sentence you have:

• Takva me komplikacija još uvijek iznenađuje.

is perfectly natural. It foregrounds takva komplikacija while keeping me in second position, which is common for short clitic pronouns like me.

Other possible orders include:

• Takva komplikacija me još uvijek iznenađuje.
• Još uvijek me takva komplikacija iznenađuje.

These are all grammatical, but the emphasis shifts slightly.

A useful point: me is a clitic, so it tends to appear early in the sentence, not in a strongly stressed position.

Because me is a clitic pronoun. In Croatian, clitics usually appear near the beginning of the clause, often in the second position.

That is why Croatian often places short unstressed words such as:

• me
• te
• ga
• je
• se
• sam
• ću

very early in the sentence.

So even though an English speaker may expect something more like Takva komplikacija još uvijek iznenađuje me, Croatian strongly prefers the unstressed pronoun earlier:

• Takva me komplikacija još uvijek iznenađuje.

Yes. Iznenađuje is the present tense of iznenađivati / iznenaditi, and in this sentence it means:

• surprises
• or, depending on context, is still surprising to me

Croatian present tense often covers both simple present and a present-state idea that English might express in different ways.

So this sentence can feel like:

• Such a complication still surprises me
• I am still surprised by such a complication

The first is the more direct grammatical match.

Here it matters a little.

Croatian verbs often come in aspect pairs:

• iznenađivati = imperfective
• iznenaditi = perfective

The form iznenađuje belongs to the imperfective verb, which is natural with još uvijek because it describes an ongoing or repeated state:

• it still surprises me

A perfective present form would usually have a future meaning in Croatian, so it would not fit as naturally here.

Croatian has no articles like a or the.

So takva komplikacija does not explicitly mark definiteness the way English does. The exact interpretation depends on context.

Possible English translations include:

• Such a complication still surprises me
• That kind of complication still surprises me
• A complication like that still surprises me

The context tells you whether the speaker means a general type or a specific situation.

Yes, depending on context, iznenađuje can be translated a few different ways:

• surprises
• astonishes
• catches me off guard
• is surprising to me

The most neutral and direct translation is surprises me, but English choice depends on tone. If the context is stronger or more emotional, astonishes me might fit better.

You would make the subject plural, and the adjective and verb would agree with it:

• Takve me komplikacije još uvijek iznenađuju.

Changes:

• takva → takve (feminine plural)
• komplikacija → komplikacije (plural)
• iznenađuje → iznenađuju (plural verb)

The object pronoun me stays the same.

It sounds neutral and standard. It is not especially formal, and it is not unusually literary either.

A native speaker would understand it as natural standard Croatian. The phrase još uvijek may sound a little more deliberate than just još, but it is still completely everyday language.