I wouldn't blame anyone for not looking back after viewing one or two episodes. A show isn't for you of a show isn't for you.
However, I don't like to judge a show's quality based on one or two episodes. I may stop watching it like I've done with plenty of shows but I wouldn't say whether it's good or bad based off a couple of episodes. This show had twenty episodes so you'll only have 20 percent of the show and you'll be missing a lot of context.
As much as I like Grimm, I could argue that's it's not very good based on a couple of episodes or I could think a show is much better than it is by only watching a couple of episodes.
Some of my favorite shows have not started off so well. For example, I enjoyed Agents of Shield and Gotham more than Grimm but I wouldn't have said that if I were just going off of each of the shows' first handful of episodes or maybe even the entire first seasons. In particular, I think AoS is easily superior to Grimm over the course of its run.