Simply put the Cowon V5 is a really nice upgrade to the O2. The V5’s form factor is similar to O2 but it’s a bit thinner and it feels sturdier. Not that the O2 had a bad build quality, but the V5 feels more dense and less hollow compared to the V5- plastic, buttons, and screen remain more or less identical.
However, the big news is how well it handles 720p content and its robust HDMI and component out video out. The O2 worked, but it wasn’t as smooth as the V5 and there were always issues with trying to get the screen sized right for the TV you plugged it into. The V5 is straight forward HDMI plug and play with the optional cable. This is no longer a sketchy dongle (lol), it’s a rather robust proprietary plug on the player itself, rather than micro-usb-ish plug seen on other Cowon players.