I thoroughly recommend portal 2 over its original, which seems needlessly complex and has none of the humour of portal 2. Some portal single user challenges are not with bothering with.
I have not tried multiplayer mode, and the challenge maps strike me as hard work or you had to be the level designer to pass.
I recommend portal2 over portal
Next for me is an add-on to portal2 mel stories which microsoft and sony drm users cant get which shows consoles suck. Stay tuned.