Not hugely familiar with Belfast but I also enjoyed Kelly’s Cellar and there’s one of those Mourne Seafood Restaurants beside it. The Cathedral Quarter a couple of minutes walk away seems to be decent for restaurants and bars generally.
I guess that Titanic Museum place might be okay for a few hours but I thought it was a bit boring myself. You might enjoy a black taxi tour of the main republican and loyalist areas and the associated murals etc. Maybe guess which side the driver’s on as invariably tries to be very neutral when driving you around.
Go for a few pints on The Falls or go for a look out at Stormont or head out for a stroll around by Queen’s maybe.