For a while now, Steam has featured game demos – tiny, curated slices of games available to download separately from the whole thing, just to give prospective players a taste of what they're like (and if their system can run them). The issue was that only a select few games offer demos, and they often feature limitations or differences from the main game that eat up valuable development time and/or offer the wrong impression. "No more," I imagine Gabe Newell saying from atop his colossal pile of money.
Steam is now offering game trials, which let you download and play the full game for an allotted amount of time. The very first game to get this treatment is the acclaimed Dead Space remake, which will serve to test the waters for this new feature and gauge player interest – so if you've ever wanted to dip your toes into spacefaring body horror, there's no time like the present. As the service rolls out, more games will hopefully begin to adopt it, especially given the fact that it's all handled from Steam's end with no special impetus put on the developer. I personally love the idea of being able to try before you buy, especially with the rising prices of video games nowadays.