I'm not sure he's that great either, but if you can get a reasonable 100 game B or C grader from any pick outside the first round, that's a decent result. If you took Hartunt with pick 5 you'd be disappointed regardless; at pick 65 he'd be a really big win.
Think of the over/under rated in terms of "is there 23 guys better than Hartung in that draft pool". I reckon about 10 (Zerrett, Fanta, Ben Brown,Lobb, Lewis taylor, maybe Dumont, Sam Lloyd, Charlie Cameron, Ambrose - a few others are arguable) jump ahead of him, and about 5 (Scharenberg, Freeman, Ben Lennon, Aish, Jack leslie, Apeness) drop behind.
So he was taken very slightly early, even with the benefit of 20/20 hindsight. Wouldn't call him a fail pick.
Overall 2013 seems pretty deep with about 45 guys having established themselves so far.