Where do I start. Holy smokes this is an incredible bike.
This is the most all-round capable bike I have ever ridden. If you are reading up on this bike, which I assume you have been, most have commented on it's ability to climb as well as absolutely crush descents. I am here to tell you it's all true.
First off, this bike isn't particularly light. But it doesn't need to be. It is incredibly efficient at climbing. You may not be the first to the top of the hill, but downshift and just pedal and the HD3 will get you there without much fuss. I get to the top efficiently, passing smaller travel bikes like it's nothing, spinning happily along on the dinner-plate of the eleventh gear. Then, when you do make it, the beast is unleashed.
Open up your lockouts and let the monster out of the cage. Holy crap is this thing fun. I have never had a bike that can handle the kind of terrain i've thrown at the HD3. In fact riding with an experienced group taking my time down rock gardens and picking my lines, a fellow rider asked what I was doing. "You don't need to be picky with that thing man....send it". He was right.
The key to this bike is to unleash it. Point it (responsibly, it's not going to ride itself) and send. The bike is VERY stiff, and that's good. The compliance is incredible and it does exactly what you want it to.
I built mine up with SRAM x01 (better gear range than shimano) 160mm Pike up front, stans flow wheels, CC inline rear shock, ks lev seat post, ibis carbon bar, thompson stem, and sram Guide brakes (love 'em). My one recommendation is to go with the Rockshox Reverb Post, it's worth the extra money. Also the stock ibis seat is garbage.
If you are looking for a bike that can climb with cross country bikes, and descend with downhill bikes, and put a grin on your face every time you take it out, you would be hard-pressed to find a bike that fit's the bill better.