I've just given the LINE6 HD units a workout @ City Music (it's yesterday actually) to hear what the buzz's about. According to the manufacturer, the HD manifestations are the company's refined LINE6 range of multi-effects, voiced to be more organic than their last effort.
The HD units feature a very user-friendly working control panel, it's like accessing your amp with some additional knobs so if you think you are too old for some digital mambo-jumbo (or too lazy for that matter), the HDs would be a different appeal. The tones on offer are more organic as promised but still lack that analogue-dynamic relationship in a non-digital set up. Despite this very minor lackluster, the HDs' on-board voicings are indeed the standard to beat; personally, I find them appealing. There's also an external loop feature in case you wish to rope in your pedals into the mix. The interface panel helps by keeping the display objective- it reflects whatever tweaks you dial in. I could safely say that the HD units are for the LINE6 lovers who could do better with less programming & more live tweaking during play. Of course, this is the best time to consider any of the models on offer since they are clearing at SALE prices, just visit City Music's showroom to hear them in action.
On a personal note, it's more fruitful for you to visit the store on a weekday instead when there is a lesser probability of being in the same room with old geisers who are more inclined to boss around during try-out time instead of making an actual purchase.