Are you talking about PC games?
Of course it depends on what you like, and even though I played Fallout 1 (I assume you played 3) I have never even heard of Portal or Metroid, so maybe we have different tastes altogether.
If you’re into RPGs:
I got Oblivion when it first came out and still haven’t found time to play (I’m sort of looking forward to an early retirement for things like this, because even a 2-week Christmas break doesn’t seem enough). I loved Gothic 1&2 (though 3 was very buggy). I got really emerged in their world.
If you’re into TBS:
I tried the latest Civ, but even though I loved Civ1&2 and Alpha Centauri, it seems that it’s just the same game with different graphics, and it was never about the graphics, so it’s just boring. The game I’ve been playing lately is Heroes3 (the series recently released number 5, but I liked 3 better).
Casual gaming: I downloaded “Magic Farm” for my daughter and got completely hooked. It’s even free (but you get ads if you don’t pay). And there’s also “Grimm’s Hatchery” which is the same thing but with dragons.
My favourite game of all time was Frontier:EliteII on the Amiga (which I played non-stop for 7 years!), but I assume you have no idea what the hell I’m talking about, and I’m pretty sure you have no PC old enough to play it.