Most of the games people think are original aren't very original, just less frequent. Portal isn't original, its just a type of gameplay(no enemies, logic puzzles) that no ones been interested in for 10 years.
Theres no originality in ANYTHING, take billions of people, give them something new to play with/make/design, wait 10 years, see that theres nothing original being made anymore, thats life.
Books, literature, poetry, theres smeg all original, just new combinations of old idea's, some of these will be interesting, others will be terrible, some will be great but you've read a book thats almost identical so you'll hate it while another person hasn't read that particular book and finds it brilliant.
Portal, it was novel, I liked playing that type of game after so long of not playing a puzzle game, and I enjoyed it, and no, I can't name what games its like, older members surely could, I have a horrific memory for names of games, and infact, my younger life, I have a really strange memory, names of people, doesn't happen, faces, always remember.
I think the people who thought Portal was the most original game ever and the best game they'd played in ages, well a "lot" of them were younger people who started gaming with COD/MOH.
Gameplay, I don't think I've played anything "new" in 20 years, great games, play them all the time, its not about how you play, but why mostly, the story, good story grips you and makes very average or normal gameplay feel fun. Same game with a woeful story can make the same identical gameplay seem boring or, repetitive, or dull.
I mean, books are the same, reading a good book, or a bad book, is still reading, yet the experience can be night and day.
A game doesn't need to be original(and by and large can't be anymore) to be good, its the whole package. Mass Effect 1 had so many irritating things, the slowest lifts in the known universe, yet so far in the future you wonder how thats even possible

Combat was, average at best, planet side driving, exploring, pretty awful, completely unoriginal.. story, epic, game overall, epic, game of the year, sure, game of the decade, maybe.