>そこまで美味くないけどそこそこ美味い
言い換えれば、「特別に美味いわけではないが、それなりに美味い」という意味になるかと思うので、
この「程度の違い」が、今回の質問の根本となります。
実は、こういう時にとても便利な表現があり、「good but not great」です。
こちらは、食べ物に限らず、様々な場面で活用できる表現です。
例文：
-----------------------
How was the new pizza joint?
新しいピザ屋の味はどうだった？
Eh... Good but not great.
そこまで美味くないけどそこそこ美味いって感じかな。
-----------------------
-----------------------
How's your wife's home cooking?
奥さんの手料理は、どんなもんだい？
In a word--good but not great.
簡単に言えば、そこまで美味くないけどそこそこ美味い。
-----------------------
-----------------------
How was the new Star Wars film?
新しいスターウォーズの感想教えて。
Good but not great.
まぁまぁというところかな。
-----------------------
※※ただ、お店のスタッフに対して使用した場合、
どうしても多少は失礼に当たるように思います。※※
一番無難な方法としては、「そこまで美味くないけど」のニュアンスを、「完全にカットする」ことです。
すると、こうなります：
「It's not bad.」
「It's okay.」
「I like it.」
「Satisfying.」
「Nice.」
「It certainly gets the job done.」
などなど。
（どれも直訳すれば「そこそこ美味い」に近い印象です。）
"its alright" means that it is okay/average in taste.
"Its good but not as nice as it normally is." means it tastes good but it was better the last time.
It's alrightはまあまあで、平均点くらいの味です。
It's good but not as nice as it normally is.
これは美味しいけど、前回ほどじゃない、という時に使います。外れの日ってやつですね。
I wouldnt say it was the best I have ever had,it was okay.
I have had better ,but this was fine too.
"I wouldn't say it was the best I have ever had,it was okay."
You are not willing to say it was the delicious but you acknowledge that it was not bad either.
"I have had better ,but this was fine too."
You have had tastier food but you acknowledge that this food was not terrible either.
"I wouldn't say it was the best I have ever had,it was okay."
あんまり美味しいわけではないけれど、そこまで悪くないというときに使うことのできる表現です。
"I have had better ,but this was fine too."
もっと美味しい料理を食べたことはあるが、そこまで味が悪くないという時にいう表現です。
Edible = fit to be eaten (often used to contrast with unpalatable or poisonous varieties).
"The shrub has small edible berries."
synonyms: safe to eat, fit to eat, fit to be eaten, fit for human consumption, wholesome, good to eat, consumable, digestible, palatable, comestible
Are these edible mushrooms?"
To set the world on fire = To do wonderful or exciting things that cause a great or remarkable sensation in the world; to be extremely popular, famous, renowned, etc. (Often used in the negative to indicate the opposite.)
"I wouldn't be too concerned with what he thinks of you. For all his money and education, he's hardly setting the world on fire, is he?"
" As a girl, Janet dreamed of setting the world on fire as a famous actress."
Edible =食べるのに適している (対義語：unpalatable 、poisonous ).
例："The shrub has small edible berries."
類義語：safe to eat, fit to eat, fit to be eaten, fit for human consumption, wholesome, good to eat, consumable, digestible, palatable, comestible
Are these edible mushrooms?" このきのこは食べられるの？
To set the world on fire = 素晴らしいまたはエキサイティングなことをして、世界にセンセーションを巻き起こすこと。極端な話、超有名になる、など（よく皮肉って悪く有名になった人のことをいうのに使われる）
例：
"I wouldn't be too concerned with what he thinks of you. For all his money and education, he's hardly setting the world on fire, is he?"
" As a girl, Janet dreamed of setting the world on fire as a famous actress."
It is not all that means it is not very delicious.
It is okay means it is not horrible either.
Therefore this means the taste of the food is in the middle of okay and delicious.
あまり美味しくないということを意味し、それが全てでありません。
「It is okay」とは、悪くはないという意味です。
そのため、これは、普通と美味しいの中間くらいの味ということを意味します。
You can say :
It's good but not the best.
It's good but not great.
It's just nice.
It's okay.
I have tasted better.
It's not too bad.
以下のようにいうことができます。
It's good but not the best.
いいですね。最高ではないですが。
It's good but not great.
いいですね。素晴らしいわけではないですが。
It's just nice.
いいですね。
It's okay.
いいですね。
I have tasted better.
美味しかったです。
It's not too bad.
悪くないです。
"The food is decent," refers to the idea that something isn't good or bad, but somewhere slightly above average.
"The food is not too bad," refers to the idea that it isn't good or bad, but it is expressing that you probably have had it better somewhere else.
In English we can sometimes say, "Oh, the food isn't too bad, but it's not too good either."
"The food is alright," would probably be the most general way to say that the food is average.
"The food is decent"（料理はそこそこです）は、「おいしくもまずくもないが平均よりは良い」という意味です。
"The food is not too bad"（料理はそんなに悪くない）は「まずくはないが、最高においしいというわけでもない」という意味です。
"The food is alright" は「料理は平均的だ」のたぶん最も一般的な言い方です。
アメリカ合衆国 
南アフリカ 
イギリス 
