I had never really appreciated the concept of Counterspell until now. Characters that are able to see the actual spellcasting get to roll an arcana check to identify the spell, and then if any one of those characters have Counterspell, they get the option to counter it. If you fail the arcana check but are still in range to interrupt, you can still counter it, but you won't know what spell you're trying to halt.
When my wizard countered her first spell like a boss, I grinned and cheered. When she cast scorching ray and got countered, I cried especially since I cast it as a level 3 spell. There's nothing like this in BG3.