If you're having lag due to a lousy system, then you should just turn some effects off. My system is awful and can't run most new games, but after turning TF2 down to low quality textures and making it play in 800x600 resolution, it's not lagging a single bit. Sure, I don't get the best graphics possible (I've seen the ultra-high-awesome-quality-pictures floating around, and yes I'm drooling), but the game still looks really nice.

So, in my experience, this game scales really well and it's still enjoyable even if your computer generally sucks. Just don't expect to run it with the highest settings. :)

Oh, and about it tarnishing TFC's memory. TFC has been tarnishing the old Quake TF memory for years and people still play it. TF2 is, for me, much closer to the experience I had when playing old Quake TF. Sure, there are no grenades, adapt. This is a fun game, I loved old Quake TF, I totally -hated- what TFC turned it into, and now I'm finally home again, feels awesome :)

Portal still rocks though.