So I managed to get into the Desura closed beta. (Somehow.) Here's what I think about it at the moment.
The first thing you realise when have a look around is that there currently isn't a lot on at the moment. At the moment, there's downloads available for 20 mods and 1 indie game (Celestial Impact). And support for a few more mods launching via the client (GoldenEye Source, for example. Don't ask me why). Considering this is a "very early beta", it's understandable.
The profiles of the mods are mirrors of the ModDB profiles. The "Support" tab takes you to the Support section of the ModDB forums. All of the news related to Desura and the mods on it are all there, and all the comments on said articles that you made in ModDB are present and correct in Desura. When they said Desura was built on top of ModDB, they really meant it. Even the video player is near-identical, only it says "DESURA" on the top right rather than "MODDB". And there's more blue, there's videos in the banners of mod profiles and the personal profiles has a larger banner. And any links to a ModDB page links to the respective Desura page: even for mods that aren't on Desura yet (in which case, you get a polite message pointing you towards the ModDB page). Observe: Moddb.com If you're reading this on ModDB, you get pointed to the ModDB page (of the announcement that Desura invites are being sent out). If you're reading this from Desura, you get pointed to the Desura version of the same article.
The site itself, basically, is ModDB v4.1. However, the client is the main bread and butter of the project. While there's several links on the client lead to the website (which opens up within the client, powered by Mozilla's Gecko engine), clicking on a download link on a mod profile prompts the mod in question to download. And then install. (Assuming it has found the respective game beforehand. At the moment, auto-finding of games is imperfect, and manual addition of install directories is a bit buggy, but, again, very early beta.) The actual installing of the mod is automatic: as soon as it finishes downloading, it begins installing. Very easy, although to be fair, so far I've only tested it on Source mods (probably the least painful mods to install in the world). Then you're free to double click on the mod to launch it (or launch it via Steam, in the case of Source and HL1 mods).
At the moment, aside from the obvious lack of content, I'm very impressed. Sure, there's a few bugs to squish, but I wouldn't be surprised if the public beta will happen by February. Then we'll really see how the system copes.
Oh wait, the system's being tested right now, right on ModDB.
Well done Desura developers.
(Oh, and thank you very much for the invite, Desura developers!)