Looks like STALKER is having a franchise sale. I've played none of them, but I recall some bug issues and something else related to them that, at one point, I was going to wait and see if it got fixed.
So, were they patched up well? Is there mod support? Good times to be had by all?
I've not had many problems with SoC or CoP. The only bug I specifically remember is one (fairly small) room in CoP with a bunch of mutants inside that regenerate health insanely quickly unless you're inside the room. Of course, they have a range greater than the inside of the room. CS has a few bugs with its faction warfare system, notably that some bases won't have squads sent to capture them. I don't believe you actually need to use that system for much to complete the main story however. (I haven't actually finished any of the games after a combined 90 hours in them, although I am fairly close to finishing CoP but am slightly put off from progressing further due to the aforementioned room, so I'll probably just start again (again).) As for mods, SoC definitely has quite a few major ones, and CS also has a few but less so than SoC. No idea for CoP, but I haven't needed mods to enjoy any of the games.
Warning: the STALKER bundle costs more than all of the games individually, don't get the bundle.Vote for SimCity4. The others are terrible.
I own a hard copy of 4, but still. More people should own it.
How does it compare to previous Sim Ctiys?
IMO it's a lot better, and I believe does have all the systems of the other games, with much better graphics. And it has quite a huge amount of community support, with new buildings (both place-able and ones that grow natually) and overhaully stuff, such as the Network Addon Mod (which I highly recommend).