Capt. Cold is great, and I liked Heatwave. Nice casting to have the brothers from Prison Break.
I also liked that Snart trained Heat Wave to learn to repair/rebuild his own gun. Presumably Snart can do the same, so they'll always be able to replace them!
I would be amazed if the Snart's sister appears in the show like she does in the comics...
All that said, it wasn't a great episode. Snart and Heat Wave are only normal people. As Barry has said to Oliver: "It's literally like you're standing still". Barry has disarmed and zip-tied rooms full of gun toting lunatics, so I don't buy that guys with fancy guns are any kind of threat without some extenuating circumstances ie. ambush.