X是X: concession (好是好，但……)
【六58】口语格式 / fixed patterns
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Repeating a verb or an adjective with 是 in the middle grants a fact before adding a reservation: 好是好，但是太贵了 ("it's good, fine, but too expensive"). In English: "it's pretty, sure, but…", "as for big, it's big, but…".
The reservation almost always follows with 可是 / 但是 / 不过 / 就是 (就是 introduces a small snag: 好是好，就是有点远). Only the bare word is repeated: never 很 or another degree adverb inside, and with a verb 了 comes after the second one (去是去了).
It is the plain version of 倒是 (level 5): 好看倒是好看，就是太贵了. Register: spoken, natural when you weigh the pros and cons.
Examples
这件衣服漂亮是漂亮，但是太贵了。
Zhè jiàn yīfu piàoliang shì piàoliang, dànshì tài guì le.This dress is pretty, true, but it's too expensive.
这个办法好是好，就是太花时间。
Zhè ge bànfǎ hǎo shì hǎo, jiùshì tài huā shíjiān.It's a good idea, but it takes too much time.
他聪明是聪明，可是不爱学习。
Tā cōngmíng shì cōngmíng, kěshì bú ài xuéxí.He's clever, that's true, but he doesn't like studying.
去是去了，不过没见到他。
Qù shì qù le, búguò méi jiàn dào tā.I did go, but I didn't see him.
这家餐厅便宜是便宜，可是要等一个小时才有座位。
Zhè jiā cāntīng piányi shì piányi, kěshì yào děng yí ge xiǎoshí cái yǒu zuòwèi.This restaurant is cheap, true, but you wait an hour for a seat.
检查是检查了，可是车还是出了故障。
Jiǎnchá shì jiǎnchá le, kěshì chē háishi chū le gùzhàng.We did have it checked, but the car broke down anyway.
Common mistakes
✗ 贵是很贵，但…… → ✓ 贵是贵，但…… (no 很: repeat the bare word).
✗ 去了是去了，…… → ✓ 去是去了，…… (了 follows the second verb).
✗ 好是好，所以我买了。 → 好是好 prepares a "but", never a consequence (say 因为好，所以我买了).