I've been remiss in posting on LTH lately, so here is some catching up...I've been to "The Mermaid" three times now, first when they had been open for a few days (cocktail and a few snacks), then back with my wife a few days later for a full dinner, and then two days ago for a solo Sunday dinner.
I've had a great experience each time, and in full disclosure I am friends with chef Manion and a few of the staff...being in the wine industry, and ex-restaurant industry, I am hard-pressed to NOT know anyone in any given restaurant

La Sirena has a very welcoming warm ambience, due to the cozy-small space, warm reclaimed woods and angle-iron used in the furniture, floors and bar, and the old-school lighting fixtures...oh, and the friendly and inviting staff.
I've sat at the bar each visit so far, so I'm now due to go back and sit at a table or banquet to get the other experience of looking at the kitchen or out the floor-to-ceiling windows...but I love sitting at a restaurant bar. The bartenders here are very friendly and helpful with explaining the drinks and dishes, so don't be shy about asking questions.
And with that said, you've probably read enough about how Manion organizes the menu, the groovy cocktails that Justin has created, etc. So here's what I had on a few visits.

The Brazilionaire cocktail - a cachaça cocktail with bitters and such. Very refreshing, but you should be fine with lots and lots of tiny ice cubes.

Back bar, with fantastic selection of rums, tequilas, mescals, aperitifs and digestifs. I love the design as well.

Moqueca - seafood mix in savory broth, and I recommend getting a side of Farofa (toasted ground manioc) like I did. It is great as a starch to add to the broth for thickening and a toasty/savory flavor. Outstanding!

Pork Loin Milanesa with wild mushroom ragu and fried egg. I HIGHLY recommend this dish!
I've also had a few empanadas that change daily, and they are a great snack or starter to share.
Be ready to wait if you arrive after 8pm, since they don't take reservations and have under 60 seats total. Sunday was very relaxing and only half-full when I left at 8:30.
- Mark
Homer: Are you saying you're never going to eat any animal again? What about bacon? Ham? Pork chops?
Lisa: Dad, those all come from the same animal.
Homer: Heh heh heh. Ooh, yeah, right, Lisa. A wonderful, magical animal.