yes I used Google Glass for a year. it definitely obscures your vision compared to not using it.
it's funny you mention games because most games I've been playing have been moving away from having a HUD visible all of the time, and only show it contextually.
I tend to believe from other people's reports (also in this page) that Google Glass works differently from more recent systems. Translucent augmentational data, augmentational data and environment co-present and just eye-focus away in focus do not seem to obscure the vision. Personal experience, though not used at high speeds.
it's funny you mention games because most games I've been playing have been moving away from having a HUD visible all of the time, and only show it contextually.