Not only is it a good beginner camera but an intermediate and a more advanced camera as well. It will allow you to grow and not be held back by it's design and features. You'll know when you're beyond it's capabilities which might take some time. The two lenses with the kit are quite good as well. I would suggest getting a good book on the D5100 and learn it's capabilities.
Good luck with your new camera and welcome to Nikonians.