Lot of passionate arguments here both for and against SMG's acting. I feel almost silly weighing in with something so wishy washy, but my honest take is that she's quite good at any scene that's just about people interacting with other people. She's believable as a character. But I think the moment she needs to indulge in even the slightest degree of technobabble, it all falls apart for her. And that's a problem on a Star Trek show.
To be clear, I'm not a hater, of either her or the show (the show is flawed and uneven, I think, but I'm genuinely encouraged by the trend). But SMG is good at playing a character so long as the dialogue is "normal." When she has to handle Treknology terms, or even just things linked closely with Trek lore, she struggles. I mean, I don't remember what specific episode it was (it was early in the season) but every time she said "United Federation of Planets" I wanted to laugh. You could hear the acting coach or director in her mind saying, "AWE AND REVERENCE! WE NEED MORE AWE AND REVERENCE!"