I bought the Orange Box for PC when it came out but my PC couldn't run it. I got a PS3 last Christmas and Portal was one of the games on my to-do list. I was not disappointed. It is unlike any other game I've played - although there's something of Ico about it. The castle is the other character in Ico and in this it is GLaDos, the computer. The malignant atmosphere spurs you on and while it can seem confusing at first it soon becomes clear what techniques work where. A second run-through and the game seems much, much easier.
Although some people say this is a short game there are some puzzles which take a while to work out and/or complete. I'd recommend playing it through in just two or three sessions at most because some of the techniques taught in the simple first levels really only come into play later on and in surprising combinations. You need to remember them all. There's an awful platform jumping level (I think it is level 17 or 18) which took me ages to work out yet a second playthrough and there was the solution in one of the early stages.
There's a wry humour throughout, not least in the length of the levels. The first ten or so take only a few seconds or minutes each. Later levels take hours to work through and seem to be unending. Levels 18 and 19 especially.
I really enjoyed Half Life 2. It starts in the shadow of the Citadel and you know you're going to end up there at the end. But there are plenty of surprises in between. I started Episode 1 but after the energy-core levels I thought the rest was just a retread.