Rather than write a full review, I'd like to offer my personal likes and dislikes about Episode Null:
On the up-side, I'm extraordinarily pleased with how well most of the levels turned out. I think this whole mod has a unique personality and a more casual depth.
On the down-side, I'm still upset with how poorly the Pogo levels came out. They're just not fun. The entire episode could stand to be a little harder.