Hjalparfoss is a unique waterfall in the sense that it's actually two seperate waterfalls joining in a elliptical pool. You'll get a great front-on view directly from the parking lot and while walking down towards the waterfall.
Don't follow Google Maps blindly, because it might lead you to a small patch of gravel directly next to the main road. About 100 meters east of the bridge there should be a sign. Turn on to the gravel road and follow it for 1 kilometer, this shouldn't take more than 2 minutes. It'll lead you straight to the parking lot, giving you a beautiful view of the waterfall. Just follow the path and stairs down for a closer view.