Which Atom? Mostly the N270 will be fine on anything that wants around a 2.4Ghz P4 Northwood or so. Usually it's the problem of not being able to add decent graphics to Atom platforms which will slow things down further though.

Then although later Atoms, quad core, have the theoretical total performance of mid Core2 Duo, it's gaming performance will suffer due to it being well into 2010s where the single core performance wasn't the dominating factor in game performance.... and again most platforms are stuck with slow graphics.

In general then, rather difficult to take an Atom system "forwards"

edit: Allowance for RAM seems to be tight on most Atom platforms also, where you'd like 4GB you can get 2, where you'd like 8GB you can get 4, etc, also a factor in not letting it stretch up.

edit2: probably be okay on GTA4 and some of the older Call of Duty editions.

Which Atom? By "Atom" I must think of the D525..

The one I have is the Z5 8350 not the N270 or D525 or anything but I just broad brushed all of them as being similarly a bit weak... mine's stuck with the 2GB onboard as well, although I didn't see that as a problem.

I was told the machine is cpu bound and that the gpu is surprisingly more capable than you would think, although it depends on the application. Sometimes it's the former component waiting around for the latter, sometimes the latter waiting on the former etc.

Throttling or failing to wedge the boost always-open is it's own consideration too.

There's massive variance for which games play nicely. Some 2010s games are happy to run where FarCry or Crysis refuse to roll much above 20. I think GTA4 is a pushing too hard on the little fella. I'd be interested to try Bully if that has some lower demands on it.

Some related VOGONS links :
Windows 2000 or XP for a "Gaming Netbook" (no really)
Retro gaming on a netbook just got better

Yes it is 2005, but Fable the lost chapters is not that bad.

Screen resolution is also a point to take into account.
If the Z5 8350 is included in a netbook, the said netbook may have a bigger screen resolution than those with N270 or D525 ...