Maybe I'm just too used to watching dramas where the story unfolds steadily and slowly, but although I enjoyed this film, and it had a good concept, I feel like the story was a bit rushed, and that some parts were brushed over, with little expansion on the backstory beyond the bare bones of what was necessary.
The main plot twist was unexpected, but I didn't find it particularly interesting or meaningful, and it had little to no bearing on the story in all honesty, I feel like it was only there to shock the audience, but I found it to be anti-climatic.
The CGI was pretty much perfect for this. It's obviously computer generated, but as most of the film takes place in a computer generated environment within the story, it's used to help define what's real and what isn't.
I think for me personally this film lacked vitality - it tries to keep you hooked on every unanswered question and plot hole, but I can only say I was curious. Even so, although I think this film could have been better, I did enjoy it, and I thought the acting was alright too.