We went to nantcol last year and are booked in again for august.
We love it, the lane is narrow but if you take it slowly its ok. There were some quite big caravans/camper vans up there when we were there.
The stream is great for the kids, there are rope swings and a pool that is great for little boats or swimming.
It is about 20 minutes in the car to Barmouth and there is plenty to do there.
There were only about 3 showers but they are building new ones for this summer I think, the site was pretty full when we were there but we still didn't queue for long. you buy a shower card so there is enough hot water for everyone.
The family who run the site are really kind I went on my own with 4 kids and felt really welcome. We loved having our campfire in the evening too. The lovely son comes round on his quad bike to sell wood and bbq's each evening. The 3 teen girls I took with me were quite taken with him
If you like proper camping, go for it.
good luck