"I'm liking this" is perfectly correct, if the speaker is deliberately limiting the statement to the present instance. For example, I generally don't enjoy job interviews, but "I'm liking this one." It can also be used to dispell an opposite anticipation: my wife went to a sci-fi movie with me, despite being sure she would not enjoy it. She leans over and whispers, "I'm liking this." Meaning she doesn't like sci-fi, but this time only, she finds she is.
However, for general enjoyment of something habitually liked, "I like this" is the usual phrase, and "I'm liking this" cannot correctly be used.
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