Die Suppe ist noch zu flüssig, aber sie schmeckt gut.

Here noch means still.

So Die Suppe ist noch zu flüssig means the soup is still too runny / still too thin. It suggests that the situation has not changed yet, often with the idea that it might improve later.

For example, this could be said while the soup is still cooking:

• It’s still too runny, but it tastes good.

Without noch, Die Suppe ist zu flüssig simply means The soup is too runny.

Zu means too in the sense of more than is desirable.

So:

• zu heiß = too hot
• zu kalt = too cold
• zu teuer = too expensive
• zu flüssig = too liquid / too runny / too thin

In natural English, too runny or too thin sounds better than the literal too liquid when talking about soup.

Because flüssig is a predicate adjective here, not an adjective directly before a noun.

After verbs like:

• sein = to be
• werden = to become
• bleiben = to remain
• schmecken in expressions like gut schmecken

German adjectives do not take endings.

So:

• Die Suppe ist flüssig.
• Die Suppe ist gut.
• Die Suppe schmeckt gut.

But before a noun, you do need an ending:

• die flüssige Suppe
• eine gute Suppe

Because Suppe is a feminine noun in German.

That is why you get:

• die Suppe
• later sie to refer back to it

Even though English uses it for soup, German uses the pronoun that matches the noun’s grammatical gender:

• masculine noun → er
• feminine noun → sie
• neuter noun → es

So in this sentence, sie means it, not she.

Because the subject is sie, referring to die Suppe, which is singular.

The verb schmecken must agree with the subject:

• ich schmecke
• du schmeckst
• er / sie / es schmeckt
• wir schmecken
• ihr schmeckt
• sie / Sie schmecken

Since die Suppe = she/it in grammatical terms, the correct form is:

• sie schmeckt gut

Schmecken means to taste in the sense of to have a certain taste.

So:

• Die Suppe schmeckt gut. = The soup tastes good.
• Der Kaffee schmeckt bitter. = The coffee tastes bitter.

This is different from English to taste when a person tries food. In German, if a person tastes something, you often use:

• probieren = to try / taste
• kosten = to taste / sample

So:

• Ich probiere die Suppe. = I’m tasting / trying the soup.
• Die Suppe schmeckt gut. = The soup tastes good.

Sie schmeckt gut specifically talks about flavor.

• Die Suppe schmeckt gut. = The soup tastes good.

Sie ist gut is more general:

• the soup is good overall
• maybe the recipe is good
• maybe it is a good soup in general

If you want to talk about taste, schmeckt gut is the more precise and natural choice.

Because aber connects two separate clauses here:

• Die Suppe ist noch zu flüssig
• sie schmeckt gut

Each clause has its own finite verb:

• ist
• schmeckt

In German, when aber links two main clauses like this, a comma is used:

• Die Suppe ist noch zu flüssig, aber sie schmeckt gut.

This sentence has two main clauses, and in each main clause the finite verb is in second position.

Clause 1:

• Die Suppe = subject
• ist = finite verb
• noch zu flüssig = rest of the clause

Clause 2:

• aber = conjunction
• sie = subject
• schmeckt = finite verb
• gut = rest of the clause

So the pattern is basically:

• Subject + verb + ... , aber + subject + verb + ...

That is very typical German main-clause word order.

Yes, flüssig literally means liquid or fluid, but with soup it is usually understood as too runny or too thin.

So a more natural English rendering is:

• The soup is still too runny or
• The soup is still too thin

German speakers do say zu flüssig for soup, but depending on context you might also hear:

• zu dünn = too thin
• zu wässrig = too watery

Yes, absolutely.

Both are possible, but they feel slightly different:

• zu flüssig = too liquid / too runny
• zu dünn = too thin
• zu wässrig = too watery

For soup, zu dünn is often especially natural in everyday speech.
So these are all possible depending on what exactly you want to emphasize.

Because gut schmecken is a very common and neutral way to say something tastes good.

• Die Suppe schmeckt gut. = The soup tastes good.

You could also say:

• Die Suppe schmeckt lecker.

But there is a slight difference in tone:

• gut is very common, neutral, and widely usable
• lecker is also common, but a bit more directly about tastiness and can sound slightly more informal

So schmeckt gut is an excellent standard phrase for learners to know.