The game is only 3-4 hours long? 
-Innuendo
If you already know the solution to all the puzzles and everything, sure. Depending on your skill level and other factors (like if you get stumped on a puzzle for a while), I'd guess a more casual first-time playthrough could take up to six or seven hours.
The game stands very well on its own two feet and doesn't feel short to me. It seems to me like reading a book or watching a movie. One with a fun story that nicely wraps everything up but leaves a hint of a possible sequel (which has since been announced).
The beauty of it being so relatively short is that when, a couple of months later you're reminiscing about how cool the game was, you can play the entire story in an afternoon to get a nice refresher on it.
In contrast, I loved Final Fantasy 7 on the Playstation 1, but after investing probably over 150 hours into it, I doubt I'm ever going to play it again, even though it's one of my favorite RPGs of all time and I'd like to play it again.
And really, for free, it's not like you're not getting your money's worth. If you don't like it just uninstall the entire Steam client and be done with it. No money invested, only a few hours lost, and you're done and know better. If you do like it, then you've been given what may be one of your favorite games for free. The potential cons/risks are extremely low and the potential benefits are fairly high. There's really no reason not to give it a try.
