Let’s look at them individually first.
Bruna, the Fading Light costs 7 mana to cast, but she’s a 5/7 with flying and vigilance, and has a really powerful ability. When Bruna enters the battlefield, you get to return a target Angel or Human creature from the graveyard to the battlefield. That is just as good as it sounds. This means you can bring Gisela, the Broken Blade back to the battlefield very easily if she died earlier on. So, now, we get to see what these two get to meld into.
Obviously, on paper, this trio looks extremely good. Gisela, the Broken Blade is probably good enough on her own to see play. Bruna, the Fading Light is well worth the 7 mana, too. It will be interesting to see if either of these two, or all three, become Standard-playable. The melding concept is quite fascinating. It will be quite interesting to see just how often these two will actually become Brisela. I know we’ll be seeing plenty of them in Commander.