I've spent some time looking over the various threads here on GDSE and also on the regular Stackoverflow site, and while I saw a lot of posts and threads regarding various engines that could be used in game development, I haven't seen very much discussion regarding the various platforms that they can be used on.

In particular, I'm talking about browser games vs. desktop games.

I want to develop a simple 3D networked multiplayer game - roughly on the graphics level of Paper Mario and gameplay with roughly the same level of interaction as a hack & slash action/adventure game - and I'm having a hard time deciding what platform I want to target with it. I have some experience with using C++/Ogre3D and Python/Panda3D (and also some synchronized/networked programming), but I'm wondering if it's worth it to spend the extra time to learn another language and another engine/toolkit just so that the game can be played in a browser window (I'm looking at jMonkeyEngine right now).

Is it worth it to go with engines that are less-mature, have less documentation, have fewer features, and smaller communities* just so that a (possibly?) larger audience can be reached? Does it make sense to even go with a web-environment for the kind of game that I want to make? Does anyone have any experiences with decisions like this?

(* With the exception of Flash-based engines it seems like most of the other approaches have downsides when compared to what is available for desktop-based environments. I'd go with Flash, but I'm worried that Flash's 3D capabilities aren't mature enough right now to do what I want easily. There's also Unity3D, but I'm not sure how I feel about that at all. It seems highly polished, but requires a plugin to be downloaded for the game to be played -- at that rate I might as well have players download my game.)

For simple & short games the Newgrounds approach (go to the site, click "play now", instant gratification) seems to work well. What about for more complex games? Is there a point where the complexity of a game is enough for people to say "OK, I'm going to download and play that"?