Let's start with the filesystem structure of Rockbox. Initially, it's hard to actually notice that Rockbox is more than just an open source jukebox firmware because like windows XP, Rockbox likes to hide a considerable amount of the system from the user. In order to disable this 'feature' you have to configure the 'file view' format to display all files and folders. Note that there is no loss of functionality when using the 'nanny' display mode. Plugins and themes are accessible from the main menu.
Reminds you of windows, doesn't it?
The manner in which Rockbox organized the OS is rather disappointing. Everything is dumped into the "rockbox" folder and there is no real separation between different types of files and folders. I would much prefer if Rockbox separated all files/folders into system files, user configuration files (system settings and themes would be held here) and applications. At present the application configuration and save files are all saved in the root plugins folder, so enjoy having highscore files littering your plugins folder. To be fair, Rockbox isn't large enough to have any 3rd party developer and its primary purpose is that of media play system, so I guess the devs see little reason for implementing a saner folder structure and proper package management. Nevertheless, it would be nice to have this issue fixed.
One of the most significant advantages of the Rockbox firmware is the way in which it implements connections and disconnections with the host computer. The iRiver firmware would hang on the 'disconnected screen' after you would disconnect the player from your computer. In contrast, the Rockbox firmware almost instantaneously becomes usable after being disconnected from the host computer.
Rockbox features a very primitive form of filetype icons. While they are quite small even when using a theme with a large font size, they can be useful.
The file type icons in Rockbox.
Games & Applications
Perhaps the most famous thing that Rockbox is known for is that with Rockbox you can play Doom on your player. You can even play half-life (sort of), by getting a half life mod for Doom. Sadly I can't get any good quality screenshots of the game in action, but if you want to see a decent demonstration of Doom on Rockbox, I suggest you check out this video. Although it might seem quite impressive at first, I must say Doom for Rockbox is a bit overrated (at least on my H340), the game is a bit too pixilated to be fun and the controls are a bit awkward. To each his own I guess. The games that I enjoyed playing the most where bubble and snake. Their simplicity is a great advantage considering the limited controls of the H340. A note of warning, Snake 1 (the 'old skul' version) doesn't seem to save high scores.
Here is a sample of games that come with Rockbox:
* Brickmania * Bubbles * Chessbox * Doom * Minesweeper * Snake * Solitaire * Space Invaders
Trust me, these games are much more fun than Doom when played on a portable media player.
Rockbox also has a gameboy emulator that allows you to play gameboy ROMs with the extension .gb and .gbc. While this is a potentially useful application that would allow users to play a whole host of new games, at present the implementation is not very usable. It doesn't seem to be optimized and at times games lag up. I have only tested a gameboy colour version of Super Mario, maybe grayscale ROMs would work better.
The Super Mario loading screen.
Rockbox also features several productivity applications. These include a text editor, a calendar application, a word clone and a paint clone. While these applications are great showcase for what can be done with the iRiver 340's hardware, I didn't really find these applications useful. The limited controller of the iRiver is simply not suited for text manipulation. In particular, I found the 'paint' application a real pain to use. Feel free to try the application out, maybe you will find them useful.
The calendar application and the Paint program
Overall, I would say that Rockbox is a more viable platform than the official iRiver firmware. I highly doubt that iRiver will release any more significant updates to its firmware and it is almost guaranteed that they will never add all the features present in Rockbox. Granted, the iRiver firmware is a lot more stable, Rockbox has a tendency to die on you, but luckily this usually happens when you're trying to load an application. In my experience, audio playback is quite stable in Rockbox. Another annoying point is that Rockbox isn't completely usable out of the box. You need to get experimental builds to get colour working in every section of the firmware and you need to get custom a custom themes pack. Hopefully all these issues will be resolved by the time the stable version of Rockbox for iRiver is released.