kono syousetu ha sukosi taikutu desu ga, saigo ha omosiroi desu.

They are marking two different topics or contrastive topics:

• この小説は = as for this novel
• 最後は = as for the end / as for the last part

In Japanese, は does not just mean the main topic of the whole sentence. It can also highlight a part for contrast.

So the sentence feels like:

• This novel is a little boring, but
• the ending is interesting.

The second は especially gives a contrastive feeling: the novel may be boring in general, but the ending is a different story.

Yes, in this sentence が works like but and connects two contrasting ideas:

• 少し退屈ですが
• 最後は面白いです

So the overall structure is:

• It’s a little boring, but the ending is interesting.

A useful thing to know is that が can do more than one job in Japanese. Sometimes it marks the grammatical subject, but here it is a conjunction meaning but.

In polite style, it is very common to attach it directly after です:

• 退屈ですが

This is a very natural pattern.

Because 退屈 is a na-adjective, and な is only used when it directly modifies a noun.

Compare:

• 退屈です = it is boring
• 退屈な小説 = a boring novel

So:

• before a noun: 退屈な
• at the end of a sentence: 退屈です or 退屈だ

That is why 退屈なです is incorrect.

面白い is an i-adjective. An i-adjective can stand by itself:

• 面白い。 = It’s interesting.

But in polite speech, Japanese often adds です:

• 面白いです。 = It’s interesting. / It is interesting.

So:

• plain style: 面白い
• polite style: 面白いです

The です here adds politeness; it is not changing 面白い into a noun or anything like that.

少し means a little or somewhat. Here it modifies 退屈です:

• 少し退屈です = is a little boring

It softens the statement. Instead of saying the novel is simply boring, the speaker says it is only a little boring.

That makes the sentence sound less harsh and more balanced, especially since the second half is positive.

Here 最後 means the end, the ending, or the last part.

So 最後は面白いです means something like:

• the ending is interesting
• the last part is interesting
• it gets interesting at the end

It does not mean finally in the sense of a transition word like at last. It is a noun here.

The は after it gives contrast:

• the novel overall is a little boring,
• but the ending, at least, is interesting.

Japanese often leaves out subjects and objects when they are understood from context.

In English, we might say:

• It is a little boring, but it is interesting at the end.

In Japanese, once この小説 has been introduced as the topic, the rest can be omitted because it is obvious what is being talked about.

So Japanese often sounds more compact:

• この小説は少し退屈ですが、最後は面白いです。

The listener naturally understands that both descriptions are about the novel.

No. Standard Japanese is normally written without spaces:

• この小説は少し退屈ですが、最後は面白いです。

The spaced version is usually just for learners, to make the parts easier to see.

So in real books, messages, and essays, you would normally write it without spaces.

Yes, it is understandable and basically natural.

A more natural written form would be:

• この小説は少し退屈ですが、最後は面白いです。

That version just removes the learner-style spaces.

Depending on context, a native speaker might also say something a little more specific, such as:

• この小説は少し退屈ですが、最後のほうは面白いです。

That means This novel is a little boring, but the latter part / the ending part is interesting.

Still, the original sentence is perfectly understandable and works well for study.

Sometimes yes, but the structure changes.

With が, the contrast is built directly into one sentence:

• この小説は少し退屈ですが、最後は面白いです。

With でも, you would usually split it more clearly:

• この小説は少し退屈です。でも、最後は面白いです。

Both mean roughly:

• This novel is a little boring. But the ending is interesting.

So:

• が = smoother, more connected
• でも = more separate, more conversational

In this sentence, が is very natural.

この means this, and it must be followed by a noun:

• この小説 = this novel

You cannot use この by itself. If you want to say this one, you would use:

• これ

So:

• この小説 = this novel
• これ = this one / this

That is why the sentence uses この before 小説.