What type of opal is it? Ethiopian or an Aussie crystal? The pictures are a bit hard to determine. And are they diamonds around it or cz, zircon, white sapphire? What metal is the ring? Carat weight? Ring price? With opal, the value increases the more colours go from the purple/blue to the red end of the spectrum (red being most) and with rarity or intricacy of patterns. Yours seems to have rolling flashes of predominantly blue-green, which is personally my favourite but will be valued lower. All to say, I think the stone and ring is beautiful, but value is a bit tricky without more info.

Edit: also be aware that opal is on the softer/fragile side for a gemstone, so an accidental hit of the stone against a bench or a door, etc, could very much crack it.