It has been sooooo long since I played Half-life 2. When it came out I was totally stunned, but my PC was not quite up to scratch to play it in maximum glory. I think I had to play it at a lowly 1024x768, but I made it 2/3 or so through then got stuck without enough ammo and got upset at the section I was stuck at. Had a computer problem and was not able to continue my game. Years passed before I got a chance to try it again but got distracted so never really dug in. Next time I start it though the gauntlets are coming off! :) Plus they have that free souped up version on Steam now too for owners of the base game. Half-life 2: Update or whatever it's called.
Then there's the extremely slowly up and coming Black Mesa game, and a fan made sequel to Opposing Force called Projekt.
I was lucky having to upgrade just before getting HL2 on account of my old PC dying. I got an ATI Radeon 9600, the beefy 256mb version! Back then the 9800 was king, and was the
gpu to play Half-life 2 with. Still, the game ran pretty well on medium-high graphics.
Anyway, good luck with it :) I'd imagine HL2 still holds up incredibly well after all these years. And even on the off chance that it doesn't, the probably swan song of HL2, episode 2, is phenomenal.
I don't know about Prospekt, but Black Mesa was pretty fun, though not on the level of HL2.