A Youtube user who wants to view a video maximized needs to open it first before the option to switch to fullscreen viewing mode appears as part of the standard user interface. Doing that once may be inconvenient but manageable, but doing it dozen times a day is everything but user friendly.
Youtube TV Mode is a lightweight userscript that will automatically load videos in full screen mode. A left-click on a video loads it in a new tab in the browser. Users who do not want to view all videos in full screen mode can middle-click a video, or right-click the video link and select to open it in a new tab to bypass the userscript automatically.
The video fills the full browser window regardless of its size and the video will always be loaded in HD format if available. This happens automatically without user interaction.
The developer has added an auto-pause feature to the userscript which pauses videos automatically if the video tab is not the active tab. And since videos are opened in new tabs they are automatically paused at least for the time it takes to switch tabs. This means that video data can be buffered in the meantime to reduce the chance of lags and stuttering.
The autopause feature can be disabled on the video screen in the upper right corner. The only remaining controls are to watch the video on Youtube, which loads the video in the normal Youtube interface and the standard Youtube video controls at the bottom.
Youtube TV Mode has been only tested in the Firefox web browser. It is likely that it will work in other browsers that support userscripts. Let us know in the comments if you have tested that. Firefox users need to install the Greasemonkey extension or Scriptish before they can install the userscript in the web browser.