This anime is one of my favorites. I have laughed, cried, and felt so many emotions from watching it. The cool part is that we could definitely have mmorpgs like this very soon where we could put on a headset and go into a world. All the seasons and arcs in the seasons are great. I think that my favorite has to be the first season in entirety, however close second is the Mother Rosario arc it made me cry so hard.
I find the third season to be very different for the first two seasons, but I think it also shows it's not different at the same time. It is definitely a good Anime to watch. This is on my recommendation list!