I had been to many water park and fantasia in patna would be in last position among all.But still as its 1st in Bihar I can say its ok.
1 thing is sure that the promoters were in hurry to open it.Except for water slides nothing looks complete.Parking not completed, you have to park vehicle on the field, approach road in bad condition.Not a decent cafeteria, just a cafe selling ice creams and chips and some other items.
Also looks that safety is there least concern, saw electrical wires with open joints, stairs to top of the slides were too slippery.Overall if you have been to any other water park earlier then you may not enjoy much but if its your 1st chance then its worth.