I doubt it, might be playable if you turn everything down, but the game is much more powerful than halflife (well it requires better hardware). Regardless of what you turn down I know you need more than a 2500+ to be smooth. And I'd recomend at least a gig of ram. I've played it and HL2 on a 2000+ with 512 megs of ram and then upgraded to a gig and there is an especially long wait time on loads if you dont have a gig of ram. I've also seen the game on a 2500+ and now on a 3400+. The 2500+ has the same laggy feel to the game, not as bad as my 2000 but pretty bad. 3400+ runs it absolutely fine without a hitch. And yes I turned down every setting to the very bottom and it didnt run well on my 2000+. Btw both setups were paired with 9800 pros. Now haveing a directx 8 card might make it run better without the new visual elements that it turns on with a newer card.
As far as gameplay goes, its a lot better than anything else that has come out this year. All the rpg elements are there and they work really well, alot of innovative character interaction. The biggest problem is they got seriously lazy when making it. The further you go into the game, the more bugs you will find. Quite possibly one of the buggiest games I've ever played. Seriously looks like they never playtested it, because some are quite obvious. Regardless of the problems the game is better than doom3 and if it was without bug would be better than hl2 by a lot. As it is I just play it more than hl2 because its more fun.