Learn Hardcore Japanese: sobo ha hudan genki da ga, kyou ha guai ga amari yoku nai mitai. - My grandmother is usually energetic, but she doesn’t seem to feel very well today.

祖母は sets “my grandmother” as the overall topic.
今日は is a contrastive topic: “as for today (in contrast to usual) …” So the sentence means: as for my grandmother, she’s usually fine, but as for today, she seems not to be feeling well.

What does だが mean, and how is it different from でも or けど／けれど(も)?

All mean “but,” with register differences:

だが: formal/written tone.
でも: conversational; usually starts a sentence/clause.
けど／けれど(も): clause-final connector in speech; polite versions pair with です/ます (…ですけど). In casual speech here, だけど is more natural than だが.

Why is there a だ after 元気?

元気 is a na-adjective. When used predicatively, it needs the copula:

Plain: 元気だ
Polite: 元気です Before a noun you use 元気な (e.g., 元気な祖母).

How does 普段 differ from いつも?

普段 = “normally/as a rule.” Good for contrasting with a special case (like “today”).
いつも = “always/usually,” emphasizes frequency or constancy. Here 普段 supports the contrast with today.

What exactly does 具合 mean, and how is it different from 体調 and 気分?

具合: “condition/working state” (of the body or even machines). Collocation: 具合がいい／悪い.
体調: “physical condition/health state” (more medical/formal). 体調がいい／悪い.
気分: “feeling/mood” (subjective sensation; often nausea/dizziness). 気分が悪い = “I feel sick/dizzy.”

I see two が in the sentence—are they the same?

No.

In だが, が is a conjunction meaning “but.”
In 具合が, が is the subject marker: “the condition is not very good.”

What does あまり mean here?

With a negative, あまり means “not very/ not much.” So あまりよくない = “not very good.” Note: With a positive verb/adjective, あまり usually needs にも to mean “too/excessively” (あまりにも).

Why is it よくない and not something with いい?

The adverbial/negative forms of いい/よい are irregular:

Adverb: よく (not いく)
Negative: よくない (plain), よくありません (polite) Spelling is commonly in kana: よくない (kanji 良くない is also acceptable).

Could I say 具合が悪い instead? Any nuance difference?

Yes.

具合が悪い is a common, direct way to say “feel unwell.”
具合があまりよくない sounds a bit softer/milder (“not feeling very well”). Both are natural.

What does みたい add, and how is it different from らしい／ようだ／そうだ?

It marks inference/appearance:

みたい: casual “seems/looks like” based on the speaker’s impression/evidence.
ようだ: similar meaning but more neutral/formal than みたい.
らしい: often hearsay (“I’m told that…”) or “typical of” sense (子どもらしい).
そうだ has two uses:
- Appearance: 悪そうだ (“looks unwell” based on appearance).
- Hearsay: 悪いそうだ (“I hear she’s unwell”).

Is ending with みたい (without だ) okay?

Yes. Sentence-final みたい (without だ) is very conversational.

Slightly more standard: みたいだ
Polite: みたいです

Is the register mixed here? だが feels formal but みたい feels casual.

Yes, it’s a bit mixed. More consistent options:

Casual: 祖母は普段元気だけど、今日は具合があまりよくないみたい。
Polite: 祖母は普段元気ですが、今日は具合があまりよくないようです。
Formal plain/written: 祖母は普段元気だが、今日は具合があまりよくないようだ。

Can I use 祖母, おばあさん, or おばあちゃん interchangeably?

Not quite:

祖母: neutral/formal “my grandmother” (refer to your own family in neutral/humble style).
おばあさん: someone else’s grandmother; also a polite way to address an elderly woman.
おばあちゃん: affectionate/familiar (“grandma”); used within the family or to address her directly.

Could I say 普段は here? As in: 祖母は普段は元気だが…

Yes. 普段は makes the contrast more explicit (“as for normally, [she is] healthy”). Without は, 普段 works adverbially and sounds a bit lighter.

Why is 具合 marked with が and not は?

が marks it as the subject of よくない (“the condition is not good”). You could use は to make it a contrastive topic: 今日は具合はあまりよくない (implying “at least regarding her condition…”), but 具合が is the default.

Can I change the word order, like 今日は祖母は具合が…?

Yes, several orders are possible:

祖母は今日は具合が…
今日は祖母は具合が… Both are grammatical. Putting 祖母は first keeps the overall topic clear; fronting 今日は emphasizes the contrast with “today.”

What level of certainty does みたい convey? What if I know for sure?

みたい expresses tentative inference (“seems/appears”). If you are certain, drop it: 今日は具合があまりよくない。 If it’s based on hearsay, use らしい／そうだ: よくないらしい／よくないそうだ。

How do you read the words?

祖母: そぼ
普段: ふだん
元気: げんき
今日: きょう
具合: ぐあい
あまり: あまり
よくない: よくない
みたい: みたい
だが: だが