Llanberis is only a small village that is not as geared up for tourists as its close neighbours such as Betws y Coed is. But as its closer to the mountains it tend to attract a lot more serious walker/climber types rather than family holiday or stag do's. Theres a few pubs that do food, the recently reopened Heights Hotel is making an attempt at doing good pub food in very pleasant surroundings, its your best bet for a decent pub meal. Petes eats will always be an option if your starving, don't have much cash and are not looking for michalin star!
The mountains are all easily accessible and theres a lovely area down at the far end of the lake which is great for kids with lots of picnic tables and shallow water for swimming. Take some shoes for the water though, its all the slate waste on the lake bottom so can be sharp. Theres also a couple of great museums, elecrtic mountain and the slate museum which are worth a look.
All in all a great place to spend a few days.