I really enjoyed watching this. I would recommend it to for people that like some slow-paced-ish stories. It's very relaxing.
Sure, the main character is powerfull to a crazy level despite being only a slime. But that's alright. This is not a story about an underdog rising to the top. This story is more about world building.
Also, some people are saying that Rimuru's voice grates on their nerves, but I dunno. I kinda enjoy it, it's relaxing somehow.
I'd say go watch it, but again don't except anything like Naruto or Hunter X Hunter.
While I wait for the third season, I'll go order the light novels.