Formal:
* Isso foi bom. (This was good)
* Aquilo foi bom. (That was good)
* Foi bom. (It was good)
Informal:
* Isso foi legal! (That was cool!)
* Isso foi ótimo! (That was great!)
* Foi maneiro! (That was awesome!)
* Foi show! (That was awesome!)
More specific:
* Isso estava delicioso! (That was delicious!) - for food or drinks
* Isso foi muito interessante! (That was very interesting!) - for something you found intriguing
* Isso foi muito útil! (That was very useful!) - for something that helped you
* Isso foi muito divertido! (That was a lot of fun!) - for something enjoyable
The best option for you will depend on the situation and your relationship with the person you are speaking to.