Like Mosi says, it's an adjective, to be specific, a participial adjective (an adjective deriving from a past participle). Present perfect active example: "Recently, I have been very impressed with the quality of the answers on Italki." (impressed describes "I") Present simple passive example: "Every time I visit Italki forums, I am impressed by the the quality of the answers." (= The quality of the answers impresses me)

when you say "am"you speak about presdnt.impressed is adj here.

You can easily say "Sono impressionato".

I am not an advanced Italian speaker but I think it is: Qualcosa mi ha colpito. (Literally = Something struck me) An Italian may be able to give you a better answer.