A game I just finished roughly in about 2 - 3 hours (the difference being all the "figuring out" time), Portal is a game certainly worth owning.
This is from a person who blindly bought Portal 2 without any prior knowledge of its earlier surprise success or without the imagination necessary to fathom how "portal mechanics" in of itself, without any other additive, be a good game.
Though I enjoyed the pacing, character dynamics, and indirect indie movie-like world building in Portal 2 more, going back to see how it all began will help explain particular jokes and flesh out many of GlaDOS's warped programming. If there's one complaint about Portal it's that, yes, it's a bit short even if for $10 but it's not like you aren't gettiing your entertainment/experience value and its chock full of special features for further insight if that's your sorta thing (it is to me!)
One complaint that might not bother others but sorta bothered me - again because I'm comparing it to 2 instead of vice versa - is that the game wastes no time piling complexity at you versus in #2 how it could often blend world building and exploration more frequently. It's a case of tight budgeting vs. free property reign but I feel it should be addressed.
All in all, Portal again cements Valve's rep at never offering inept neurally challenged games. Believe the hype or challenge it, either way, playing any entry from the series will add something you'll cherish in your life.