Spent many long weekends here as a tent camper over 6 years, being in close proximity to Philadelphia. Timberline lake serves as a seasonal resort, but also a small trailer park. The staff have always been friendly & have done their best in my experience to be accommodating. The seasonal and full time residents are friendly and helpful as well. Check their website for the weekend activity lineup. We've enjoyed their movie nights on the beach and when they host beach parties with the "party time djs." There's a shop and small game room with a bad pinball machine but legit air hockey table. There are some new swings at the playground. The main bathroom isn't the cleanest but certainly isn't gross, either. I find it sub par for a campground.
The lake is my biggest draw if you're an avid swimmer and want to get some uninterrupted laps in. The cedar water is always warm and it's never crowded in the deeper area. The beach is kept up. You can rent canoes for $5 per 30 min, but there aren't many places to row to. Still nice though! It's also a pleasant walk around the lakes where you can spot carnivorous plants, frogs and turtles; perhaps even pick wild blueberries. There's usually a nice breeze across the dikes and the sunsets are swell too. Never had a problem with bugs or wildlife, but have occasionally spotted wolf spiders on our tent, once saw a bushy tailed fox, and even a daddy long leg feasting on a tiny dead garter snake! You are in nature. Check for ticks.
Most of the spacious pop-up/tent sites are among pine trees surrounding an open field. It's not too wooded, so your site is likely to receive a lot of light AM to PM. However, less wooded also means slightly less privacy, but they're spaced out enough that I haven't found it to be a problem. These sites sit closer to the somewhat busy road (at least in the summer) so if you're able, reserve a site that's behind the field, towards the walking path.
There are also some lake front sites, but I haven't stayed there. They look nice and you're less likely to hear traffic from the road, however you're closer to the RV/trailer sites, so you might hear music and people during the day into night till quiet hour. I'm just speculating, though. I haven't found any of my stays to be too noisy. Avoid the site next to the office as its by the vehicle entrance and is along the road.
The only drawbacks I can find are some of the seasonal/permanent residents don't care for their sites very well; some are even borderline junky. It doesn't set a good precedent and makes it less like a campground resort, imo. The tent sites could also use a raking a bit more frequently. I make sure to bring my own to clear fallen sticks and gathered leaves in order to level out the sand. Overall, I think the resort aspect of it could use a bit more easy landscaping/flowers planted in the summertime to brighten things up quite nicely. It has potential to look so great, rather than just simple. It would also be SO nice if they offered free coffee or better coffee for a small fee in the camp store, as many campgrounds do. There is $1 coffee that you wouldn't know unless you ask, but it's made to order in a single cup keurig like machine and they always use too much water. So you wait 5 minutes for a cup of coffee flavored water. It's so bad, and there's no place nearby for coffee, but the ladies who make it are so nice you don't want to tell them it's bad!
Overall, this is my go to for tent camping. It may not be for everyone, but I love it.