The Aliens seemed incredibly unbelievable to me, Why go into the past to get some of that yummy human juice they lived on? There are plenty of undeveloped planets out there. It seemed liked an story excuse they came up with to introduce Guinan.
Personally, I find it very hard to believe that a race of aliens evolved in such a manner that energy from humans was their only food source. What happened before they encountered humans ?
Was it only humans? I thought they could feed off any humanoid...
Even then, there was no evidence of humanoid life on their planet.