As the title suggests, the Archos 404 could be given anything between 1 & 5 stars depending on how you intend to use it:
Video playback is excellent, the screen resolution is flawless and bright. Sound quality is excellent too, as long as you're using headphones (the built in speaker is only really good for momentary review of sound files). The photo viewer and portable hard drive functions are excellent, though the menu system can sometimes be hard and slow to navigate.
If you're looking at buying one with the intention of using it in a 'static situation' i.e. a train commute to work or similar, then it'll prove to be a fantastic little device. However if you're intending to use it 'on the move' i.e. whilst walking/jogging, then I'd recommend looking at a different product. The Archos has a delicate mechanical hard drive and doesn't respond well to any movement.
I bought mine with the intention of using it with the accessory helmet camcorder, so a friend and I could record ourselves on our motorbikes (on road). We tried a few different methods of carrying the unit (wrapped in a thick towel in our seat units, stored in our pockets, in a rucksack etc) but the Archos wasn't happy with any of them. Each time we stopped to check what we'd recorded, the unit had locked up (which requires a needle or pin to press the reset button) and we'd lost most of the footage. We'd subjected it to no more vibration than it'd get from walking, so as I said before, using the item in anyway 'on the move' is a big no no. Also the standard of recording is poor, don't expect DVD-quality playback.
The only other gripe I have is that you have to purchase some plug-ins from the Archos website to play certain file types, and there's no mains charger supplied with the unit.