Portal is very overrated... But that's OK, it's still great.
As far as strategy- yes, Total War. TBH I'm not the biggest fan now, loved the earlier games before they bloated, but I'm in a minority. And Company of Heroes 2 is about to come out, since COH is the best realtime strategy game ever made I guess COH2 should be good. (worth buying the old one, if it came out today it'd still be a big deal)
Fallout 3/Skyrim are great exploring games- you can follow the game itself and the plot, if you like, but tbh Fallout 3 wears out halfway through if you do that. But just dicking around in the wastes is fantastic. Never played a game with such a feeling of place.
(Don't buy Fallout DLC, it's no good! Most especially, don't do anything that lets your level cap rise too high, if you get it to 30 with Broken Steel, all of a sudden most enemies turn into terrible, fun-less bags of HP and the game's shooting goes crap.)
Oh... And leftfield option, the original STALKER: Shadow of Chernobyl, and mod the crap out of it. The later games are alright but SOC is something a bit special, and the graphics mods make it quite, quite brilliant.