This place is huge and offers and astounding variety of vegan ice creams, including soft serve (2 or 3 varieties), regular vegan ice cream in a cup or cone (about 12 flavors), vegan ice cream cakes, and novelty desserts. I'm not sure if this is the same as Klein's kosher ice cream or if they just buy from Klein's (which is also the ice cream used at Food Swings and other veg restaurants). As for ambiance, the place looks like a bright Candyland playground with Hebrew music playing in the background. Seriously.
I got a cone with 2 scoops, which was about $3.50, which is pretty cheap. Definitely more cheaper than upscale places like Lula's and Stogo. That said, Ice Cream Castle's ice cream is made with tons of water, sugar, and I think corn syrup. The upscale places make small batch coconut, hemp, and cashew-based ice creams so you get what you paid for. I don't recall what flavors I had but I've had tons of Klein's ice cream so it doesn't really matter. They're all good (minus pistachio and coffee, in my opinion, which I've never cared for).
When I was in, the service was friendly, but I feel compelled to share an experience of a female friend that went once. She was told that she wasn't allowed to enter because she was wearing shorts and a t-shirt. As this place is run by super orthodox Jews, they have modesty laws (posted on the building!). My friend said the people were very rude and wouldn't let any women enter, but let the guys in. I didn't have any issues when I went so it may depend who's working. Some non-Jewish employees told me that sometimes the rules are enforced and sometimes they aren't.