Is Portal just a silly game thrown into a Half Life collection? No. Portal is a masterpiece.
The environment of Portal is amazing, yet so simple. You wake up in a glass chamber, and are greeted by the wonderful computer voice of Gladus. Everything is all shiny like a futuristic laboratory should look. The game looks as nice as it needs to look, and better yet, you don't need an insane graphics card to handle it.
The controls are similar to most first person shooters (though I wouldn't call this an FPS), although at times you might wish you could jump more accurately. It's not a big deal at all though.
The difficulty at the game is perfect. If you get stuck on a puzzle, your not likely to be stranded forever. You simply have to play around with the portals (and environment) until something clicks and your able to move on (hopefully). Also, there is no limit on lives, if you "die", you can simply start off close to where you left off (and you can save at any time as well).
In the end, Portal is a game that will challenge you, entertain you, and just make you laugh. There is plenty to be found, and of course there is always cake.