should I control his food intake?

My cat weighs a little over 8lbs
He is a rather tall cat, with long legs. He should weigh quite a bit more (he was a little skinny when I got him)

According to the label on the food bag, an 8lbs cat should eat around 1/2 cup of food a day. Given free access to the food, my cat will eat around 1 cup. That's the recommended amount for a 16 lbs cat!
Should I continue to let him eat all he wants? He does need to gain some weight but I don't want him to gain too much.

Each cat is different, I leave dry food down all the time and none of my cats are overweight at this time (I may need to watch Spirit in the future). Some cats will gorge themselves and not know when to stop and others won't. You could try putting out 3/4 a cup at a time and see if he starts to fill out to where he should be and not feel so hungry. Play with the amount till both of you are happy with the outcome.

I have 2 cats that tend to overeat so I do ration their food, they get fed twice daily and a certain amount. I think you just have to play around with the amount until you reach that balance. The amounts on the bags are just approximate.

Truthfully the amounts on the bag are there to sell more food, I always find them a liitle on the large size. In Marie-p's case though the cat could stand to gain a few pounds.