Well it's good, but I also think it's over-hyped just because it has vaguely darker themes. I basically enjoyed the first few episodes and the last few episodes, and felt that everything in between dragged a bit. The movie is amazing though, and managed to inject a lot more plot and personality than the show did. If your definition of "mature" toku means "blood and boobs" then yeah, you'll be happy with Garo, but if by "mature" you mean "better story telling and more depth from the characters" you're actually better off with almost any Sentai series.
My big problem was I'd already seen KR555 when I watched Garo, so I'd already been spoiled.