The size is considerably smaller than the old Q3 and the menu is much better. The sound quality is just as awesome as the Q3. There are more options for sound and video. The "onboard edit" software is better, but who cares? It will always be preferable to use a PC program to edit the videos.
Please note that it outputs/records in the seriously fucked up .MOV format. To get it transferred to a decent format like .MPG, your PC will have to sweat. It can take some time to convert video files depending on the horsepowers hidden in your CPU.
It still has a very "plastic" like feel to it, probably because it is made of plastic (a shame really, just imagine it in a titanium casing!), it has no video stabilizer and it still picks up some sound from pressing buttons etc. (no problem when recording loud live music, but still a problem though, if trying to zoom at a low volume output from the musicians.)
HD video is a billion times better than the old Q3's 640x480. It is obvious, and so is the result. Great resolution and much better than the old Q3. But honestly, do not expect world top class camera lenses/objectives from Zoom because that's not what you are going to get. You get the equivalent of the same size mobile phone with the same limited zoom capabilities (digital only). Also remember that there is no stabilizer, so if you are standing in the front row or anywhere near it, it will be "dizzy cam". In fact it will be "dizzy cam" unless you lean against a wall. As simple as that. You buy this thing for the sound, the picture is just a free bonus. But a great bonus it is in perfect conditions!
The navigation buttons totally suck compared to the old Q3. You often unintentionally stop the recording while only trying to do an innocent zoom. It is really a bad design!! I bet there will be a v1.2 at some point with different button layout. There would be, if I was in charge. The microphones are completely visible compared to the old model. In fact I think the old model was more easy to disguise as a mobile phone than the new one because of the microphone arrangement. However the grey color is a lot better than the standard medium blue of the old one. Let's face it, you are not always allowed to bring in this thing, but you are never interested in the discussion: "if you are allowed to".
I'm in total doubt about the microphones. I think they are the same. But, the old one worked reasonably well on "auto level". You had to fix a few level problems after, but not much really. The new one is worth shite on "auto". It just jumps up and down whether on one "auto" setting or the other. I only use it on low mic now. It works for most high volume rock gigs.
The Q3 and Q3HD battery consumption seem to be equal. About 2 hours of heavy usage.
Like I already mentioned, it is plastic. Meaning it is impossible not to get scratches on the device. It is some cheap shit from a hardware point-of-view, but the mic and HD video recording is what you buy it for. I'd hoped for the perfect thing, but especially the navigation pisses me off time after time and I've lost some crucial recordings already. :( Bad bad bad. Beside that, I love the device. Love - Hate relationship I guess. Bring me in as a tester next time, Zoom.
You only get the main device in the standard package, but you can buy a rather cheap extra package with tripod, bag, AC adapter, various cables, microphone wind protection etc. And really, you should!
5/6 may seem a bit high considering my comments above. But your other options are few if you want a compact device with this audio quality and HD video. Few or none.