Let us take a moment to wrap our collective minds around the fact that the abomination pictured above is, I quote, 'indistinguishable from a normal human at distances greater than 30 feet'. I'm fairly sure I'd be able to spot the difference, to be honest.
With that out of the way, let's take a look at medusas. They have six monstrous humanoid HD, which are somewhat south of a ranger's. Their ability scores get bonuses in the 2-4 range, with the exception of their unboosted strength.
Aside from that, medusae have the quite unique 'snakes' natural attack, which deals a few points of damage with moderate strength poison attached. They also have some natural armor.
Finally, their main attack. It's your typical petrification gaze, aided by innate charisma and availability of Narrowed Gaze. Useful against most stuff, nonfunctional against a few.
Having to choose between +1 and +2 LA, I think I'll settle for +1 right now. Medusas have one strong ability, but so do many other monsters, and apart from their one trick they're near-worthless. Feedback is welcome!