Depending on context it can be! But consider something like "Isn't it really interesting how X went down?". なるほど is also pretty casual, and can also imply to me

Depending on context it can be! But consider something like "Isn't it really interesting how X went down?". なるほど is also pretty casual, and can also imply to me new information. I don't want to imply I find it amusing or something positive - it might be something sad or atrocious (面白い is out). I don't want to imply I want to learn more or am deeply invested in it (興味ぶかい also out). That pretty much exhausts the available options when I've asked Japanese friends.