Ten nowy plan jest jeszcze lepszy niż tamten.

They are demonstratives:

• ten = this
• tamten = that

In this sentence:

• ten nowy plan = this new plan
• tamten = that one / that plan

Polish often uses tamten by itself when the noun is understood from context. So tamten here really means tamten plan, but plan is omitted because it would be repetitive.

Because Polish allows you to leave out the noun when it is obvious.

So instead of saying:

• Ten nowy plan jest jeszcze lepszy niż tamten plan.

you can naturally say:

• Ten nowy plan jest jeszcze lepszy niż tamten.

This works much like English this one and that one, except Polish often does not need a separate word for one.

Because dobry (good) has an irregular comparative form.

• dobry = good
• lepszy = better
• najlepszy = best

So lepszy is the normal and correct comparative form.
Using bardziej dobry would sound unnatural or wrong in standard Polish.

This is similar to English good → better, not more good.

Here jeszcze means even or still, adding extra emphasis to the comparison.

So jeszcze lepszy means:

• even better
• sometimes still better, depending on context

It does not mean yet here.
The word jeszcze has several meanings in Polish, and this is one of its common uses with comparatives.

Niż means than in comparisons.

So:

• lepszy niż tamten = better than that one

It is the standard word used after a comparative adjective such as:

• większy niż... = bigger than...
• szybszy niż... = faster than...
• droższy niż... = more expensive than...

Yes, very often you can.

For example:

• Ten nowy plan jest jeszcze lepszy niż tamten.
• Ten nowy plan jest jeszcze lepszy od tamtego.

Both mean essentially the same thing.

But there is an important grammar difference:

• after niż, you often keep the basic form: niż tamten
• after od, you need the genitive: od tamtego

So both are correct, but the form after them changes.

Because od requires the genitive case.

Compare:

• niż tamten — no case change needed here in this kind of sentence
• od tamtego — genitive required by od

This is a very common pattern in Polish: prepositions often require a specific case.

In Polish, in ordinary present-tense sentences like this one, jest is normally used.

So:

• Plan jest lepszy. = The plan is better.

You generally cannot drop jest here in standard Polish.

Polish does sometimes omit forms of to be in certain informal or special structures, but not in a normal sentence like this. So jest is necessary.

Because they all match the noun plan, which is:

• masculine
• singular
• here in the nominative

In Polish, adjectives and demonstratives agree with the noun in gender, number, and case.

So with plan, you get:

• ten plan
• nowy plan
• plan jest lepszy
• niż tamten

If the noun were feminine or neuter, the forms would change.

For example:

• ta nowa idea jest lepsza niż tamta
• to nowe rozwiązanie jest lepsze niż tamto

Yes. Plan is a masculine inanimate noun.

That matters especially in some cases, such as the accusative, where masculine animate and masculine inanimate behave differently.

In this sentence, though, the key thing is simply that it is masculine singular, so the agreeing words are:

• ten
• nowy
• lepszy
• tamten

Yes, Polish word order is more flexible than English, although not completely free.

The given sentence is the most neutral and natural order:

• Ten nowy plan jest jeszcze lepszy niż tamten.

But other orders are possible for emphasis, for example:

• Jeszcze lepszy niż tamten jest ten nowy plan.

That sounds more marked and stylistic, with emphasis on the comparison.

For learners, it is best to stick to the original order until you feel comfortable with emphasis patterns.

Normally, no. In ordinary Polish noun phrases, the demonstrative usually comes first, then the adjective, then the noun:

• ten nowy plan

This is the most natural order for this new plan.

Changing that order is only possible in special stylistic or emphatic situations, and it may sound unnatural to a learner if used randomly.

It is a predicate adjective after jest.

The structure is:

• Ten nowy plan — subject
• jest — verb
• jeszcze lepszy niż tamten — predicate/complement

So lepszy tells us what the plan is like; it is not directly placed before the noun as in lepszy plan (a better plan). Instead, it comes after jest: the plan is better.

Yes, absolutely:

• Ten nowy plan jest jeszcze lepszy niż tamten plan.

That is grammatically correct.
But in normal speech and writing, Polish usually prefers the shorter version:

• ...niż tamten.

because the noun is already obvious.

Yes.

• lepszy = better
• jeszcze lepszy = even better / still better

So jeszcze adds intensity or contrast.

Compare:

• Ten plan jest lepszy niż tamten. = This plan is better than that one.
• Ten plan jest jeszcze lepszy niż tamten. = This plan is even better than that one.

Not in this sentence, because the context is clearly plan.

Polish demonstratives agree with the thing they refer to. Since plan is masculine singular, tamten matches it.

In another context, tamten could refer to a masculine noun of a different kind, but here it clearly means that plan.

All the agreeing words would change.

For example, with idea:

• Ta nowa idea jest jeszcze lepsza niż tamta.

Compare:

• masculine: ten nowy plan jest jeszcze lepszy niż tamten
• feminine: ta nowa idea jest jeszcze lepsza niż tamta

This is a good reminder that Polish demonstratives and adjectives must agree with the noun.