Explanation
Indicates that while something may be true or valid, there is another contrasting point.
Formation
Verb-casual + ことは + が, い-Adjective + ことは + が, な-Adjective + だ + ことは + が, Noun + だ + ことは + が
Detailed explanation
The ～ことは…が grammar point is used to express that although something might be true, there is another point or fact that is being contrasted with it. It can be translated as 'it may be true but...', 'it is that... however...', etc. The formation differs depending on whether it is used with a verb, い-adjective, な-adjective, or noun.
Examples
Kono eiga wa omoshiroi koto wa omoshiroi ga, chotto naga-sugiru.
This movie may be interesting, but it is a bit too long.
Kare wa shinsetsu na koto wa shinsetsu da ga, sukoshi mukuchi da.
He may be kind, but he is a bit quiet.
Kono geemu wa muzukashii koto wa muzukashii ga, yamerarenai.
This game may be difficult, but I can't stop playing.
Kanojo wa utsukushii koto wa utsukushii ga, chotto koubisha da.
She may be beautiful, but she is a bit arrogant.
Practice
Grammar content sourced from hanabira.org.