My family and I have joined in the summer festival. We tried the horse race and the fishing quests. We intend to try out the tavern society quests.
The horse race gives you a special white lithe festival horse with a green blanket and yellow sons. The fishing quests give you fish and tokens that you can trade in for a summer festival banner for your front lawn. You can also get a special summer festival pattern for the walls in your kin house and/or personal house.
We like all these premium items.
The horse is very pretty. I guess it is a matter of taste whether you like the green blanket with the yellow suns on it. Unfortunately the horse is not any faster than a regular horse. I guess you have to build faction and buy one of the faction horses to get a faster horse.