Das Ergebnis enttäuscht mich.

Because mich is the accusative form of ich.

In this sentence:

• Das Ergebnis = the subject
• enttäuscht = disappoints
• mich = the direct object

So the structure is:

• The result disappoints me

German changes pronouns depending on their role in the sentence:

• ich = I
• mich = me

So Das Ergebnis enttäuscht ich would be wrong.

Because German main clauses normally follow the verb-second rule.

Here, the sentence is:

• Das Ergebnis = first element
• enttäuscht = finite verb in second position
• mich = object

So the word order is completely normal for a German statement.

German often looks like:

• Subject + verb + other elements

as in:

• Das Ergebnis enttäuscht mich.

Here it is a verb.

More specifically, it is the 3rd person singular present tense form of enttäuschen.

• ich enttäusche
• du enttäuschst
• er/sie/es enttäuscht

Since das Ergebnis is singular and treated like es, the verb form is enttäuscht.

This can be confusing because enttäuscht can also be an adjective or past participle in other sentences, for example:

• Ich bin enttäuscht. = I am disappointed.

But in Das Ergebnis enttäuscht mich, it is clearly the finite verb.

Because Ergebnis is a neuter noun in German.

Its article is:

• das Ergebnis = the result

German nouns have grammatical gender, and Ergebnis happens to be neuter. This is something you usually have to learn together with the noun.

So it is best to memorize it as:

• das Ergebnis

not just Ergebnis by itself.

enttäuschen means to disappoint.

So:

• Das Ergebnis enttäuscht mich. = The result disappoints me.

A useful pattern is:

• jemanden enttäuschen = to disappoint someone

Here:

• jemanden becomes mich because someone is me

Other examples:

• Du enttäuschst mich. = You disappoint me.
• Das Wetter enttäuscht uns. = The weather disappoints us.

Yes, absolutely. That is very natural German too.

The difference is mainly in focus:

• Das Ergebnis enttäuscht mich.
  = The result disappoints me.
  Focus on the result as the thing causing disappointment.

• Ich bin von dem Ergebnis enttäuscht.
  = I am disappointed by the result.
  Focus on your emotional state.

Both are correct, but the second one is often a little more common in everyday speech when talking about how you feel.

Yes. German allows some flexibility, as long as the finite verb stays in second position in a main clause.

For example, you can also say:

• Mich enttäuscht das Ergebnis.

This still means The result disappoints me, but now mich is placed first for emphasis. It can sound like:

• Me, the result disappoints

So the basic meaning stays the same, but the emphasis changes.

The most natural negation is:

• Das Ergebnis enttäuscht mich nicht. = The result does not disappoint me.

Here, nicht usually comes near the end of the clause.

If you wanted to negate the noun instead, you might say something different, but for a simple sentence negation, nicht is the normal choice.

They are capitalized for different reasons:

• Das is capitalized because it is the first word of the sentence.
• Ergebnis is capitalized because all German nouns are capitalized.

This is a very important feature of German spelling:

• das Ergebnis
• die Stadt
• ein Auto

Nouns always begin with a capital letter.

You can identify it by looking at both meaning and grammar.

In the sentence:

• Das Ergebnis enttäuscht mich

the thing doing the disappointing is das Ergebnis, so that is the subject.

Also, mich is clearly accusative, which strongly suggests it is the object, not the subject.

So:

• Das Ergebnis = subject
• mich = object

This is similar to English:

• The result disappoints me

The infinitive is enttäuschen.

That is the form you would look up in a dictionary.

So if you see:

• enttäuscht
• enttäuschte
• hat enttäuscht

you should look for:

• enttäuschen

This is a good general rule in German: when you meet a conjugated verb form, try to identify its infinitive.