I think this verb tense "has... pleased" is the present perfect tense, which typically represents an event that started in the past but continues into the present. If you look on the Duolingo web version, the tips and notes specifically mention that this is not the same tense as the German perfekt.
Technically, though, the present perfect can also represent an event that occurred at an indefinite point in the past, but "it has not pleased me" may not be specific enough to determine which it is. Here are two examples of the same tense with different meanings, clarified by adding a few words: "It has not pleased me thus far" (e.g. I'm watching a play and I don't like it so far) "It has not pleased me in the past" (e.g. I've gone to see this play several times, and I never liked it)
It has not pleased me (doesn't specify time when it happened)
It has not pleased me thus far (action which began in the past has continued to the present)
It has not pleased me in the past (doesn't specify time when it happened)
I think all of these are perfectly normal sentences in English perfect tense
it did not please me is simple past and is much more common expression in English unlike in German which prefers perfect tense to describe events of the past
gefallen is a dative verb http://german.about.com/library/verbs/blverb_dativ.htm
The subject with gefallen is actually the "es" in this exercise. While it's translated to "I did not like it" in English, the direct translation would be "It was not appealing to me".
Note that "I" is the subject in English, and "it" is the object. In German, however, "it" becomes the subject, and "me" is the object (dative here because it is "to me").