Ray of Light is pretty good.
However, it does have spell resistance and at that level, some BBEGs have things like Blur or Displacement or Invisibility or some other way to get a miss chance. They also tend to have Dispel Magic and/or Dimension Door, either themselves or a henchmen, so there are alternatives, even to being blind. This spell is probably best against monsters.
Also, at that level, the minimum range is 50 feet. At least in our game, 50 feet covers most of the battlefield most of the time considering that a spell caster could use a move action to move 30 (or 20) feet closer and then cast it.
Finally, a critical with the spell can double the duration and the spell can be Empowered as well. For a Sorcerer, this could turn out to be a bread and butter slow up the opposition type spell.
So, the spell is pretty good, but it is not in the must have category.
I also like Ray of Entropy against those nasty combatant type opponents.
And Ray Deflection is a must have for BBEGs. Be sure that the only thing you tell the PCs is that they miss, regardless of what they roll. They'll figure it out if they roll a 20, but even with a 19, they might just assume that the NPC has a huge touch AC. In fact, I could see a PC missing with a high roll like 18, and then next round using True Strike, and then with another Ray spell, missing again. Boy could that get a player upset.
