I played and beat Portal in one sitting on the day that the Orange Box came out in 2007, and I thought it was a pretty fun little surprise. Then I went online a few days later and saw people were calling it one of the greatest games of all time, and I have to say, that was a bit much for me. Portal 1 is a great game, that's definitely true, but it's far from perfect: the levels are just too easy across the board, and GlaDOS's characterization is very one-note, albeit a very good note. Highly recommended since you can get it for basically no money these days, but please set your expectations accordingly.