The best club in oslo by far if you like techno & electronic music. Comparable to Jaeger when they don't play mainstream music, just a lot bigger.
The place consists of two dancefloors with a DJ set in each. Music is loud, but not as loud as other clubs, i.e. you can actually sit and talk at a reasonable level at tables yet have fun with the music. There are also a lot of nooks and crannies with tables and sitting areas around, making it a nice place to chill even if you're not so into dancing.
Some people on here comment that they weren't allowed in for various reasons. If you're smart, you send your name (and your friends names) to their guestlist mail earlier the same day asking to be put on the guestlist, and you'll get in free of charge before midnight (as long as you're over 23). The email can be found on their event page on Facebook or on their website. Never had any issues with getting in, even after having quite a lot to drink. Be there around 23:00-23:30 to secure a table and dodge the heavy queue.
Unlike other places in town, they absolutely do not pack the place full of people, so if you arrive late or aren't on the guest list, you are at a high risk of being rejected as the place is very popular and will be full. Most people come around 23:30 to 00:30.
Drink prices are decent, and comparable, if not lower, than other places in Oslo's center. Prices include 68 NOK for a 0.4l beer (Frydenlund), 116 NOK for a vodka Redbull, and anywhere in between for better beers, cider or a glass of wine. They also offer a bottle of Cava for 410 NOK at the bar.
tl;dr Good place for underground techno/electronic music, decent bar prices, and get on the guestlist and arrive early if you want to get in. Hugely recommended place :)