I absolutely loved this series.
The story is a mix of 2 separate stories that sort of come together at the end. An explosion occurs in a classroom causing a lot of people to be reincarnated into a fantasy realm. Most end up together in a magic school where they work to hone thier skills and become strong enough to go on an adventure to find the students of the class that are still missing. The other is the tale of a girl who is reincarnated as a spider trapped in a huge labyrinth of caves and has to hunt to survive and eventaully grow strong enough to fight her way out. While both stories were interesting on their own, I wish I could have seen them come together a bit more than they did.
I understand that people have a problem with CGI animation, but I thought it worked very well for this series. Watching the spider change into various forms as she evolved and became bigger, faster and stronger was great and all the monsters she fought along the way looked fascinating. The combat sequences from this series were also excellent, especially the battles against dragons.
Voice acting was also top tier. I don't think I can even put into words how well Brianna Knickerbocker performed in her role as a spider. Listening to her voice while her character suddenly went from dancing around in glee celebrating a new skill she learned to freaking out that some new monster was trying to kill her was an absolute delight that caused me to watch every episode with a big smile. The music was also good, but immersive and not overpowering. The only bad thing I can say about the sound is that I didn't like the ED song and I thought it didn't fit the anime.
I felt like this series had a good variety of characers. The spider was a shut in type of character and vary adaptive to game mechanics which allowed her to survive in a brutal environment and grow extremely powerful. There was also a hero who didn't have confidence in his own strengh but did what he had to do to try to live up to his brother's shadow. There was a character who was reincarnated as a baby earth dragon who didn't really care about becoming powerful and just wanted to sort of go along with the flow, but was still willing to put her life on the line when her friends were in a time of need. Overall I thought this series had a good cast of characters that had enough development to be interesting but not so overly detailed that the whole story was bogged down by constant flash backs.
Final thoughts - I really hope this anime gets a second season soon because I would love to see more of what happens once the two stories intertwine a bit more. Unless another anime comes along and completely blows me away, this is my pick for anime of the year.