Don't consider any 'Once Upon a Time' episode terrible, even the lesser ones, regardless of my underwhelmed opinion on the final season. There are a fair share of very disappointing ones when the show became uneven and started feeling like a different show compared to when it first started. But also many brilliant ones, though unfortunately not in Season 7 ("Beauty" and "Leaving Storybrooke" did come closest to being great) where most of the best episodes were on good but not great level.
"Secret Garden" is a not so magical episode. Certainly watchable and terrible it isn't, but it is not great either and could have been better. Little is done exceptionally, with the high points being two good characters and their chemistry and performances, and a good deal of things didn't really work, with one subplot and two characters in particular bringing it down significantly. One of Season 7's middling-lesser episodes in my view and in the weaker half of the show.
Although her character and development improved quite vastly in "The Girl in the Tower" (where she has more personality and is less over-angsty), Robin didn't do much for me here. Didn't find myself particularly engaged or emotionally invested in her story and didn't find her relatable or interesting.
Worse is Henry and Jacinda, their complete lack of chemistry is one of the low-points of 'Once Upon a Time' and Jacinda is a contender for the show's most annoying, quite insufferable at worst, character. "Secret Garden" did nothing to change my mind, reinforced it actually. Other episodes do a much better job at advancing characters and moving plot-lines forward, with more interesting characters side-lined and too much focus on those that compel far less. All the scenes with Henry and Jacinda, primarily in the hospital, are quite difficult to sit through. Too much of the dialogue is cheesy and soapy and Dania Ramirez comes off worst of the variable cast.
Gabrielle Anwar and Adelaide Kane however fare much better, with Kane being very good and one of the season's best assets overall. Rapunzel's character development provided a lot of emotional impact and the icy tension between her and Drizella has both chills and heart. By far the most believable of the character chemistries, the only one that properly works.
It is beautifully and atmospherically photographed with settings and costumes that give a sense of wonder. The music doesn't ever sound cheap or out-of-kilter, fitting well with the mood and never found myself questioning its placement.
Concluding, watchable but also underwhelming. 5/10