Games: Any of the games that I periodically play run fine under win2K --- as I am not a big gamer, and usually run/use games that are years++ old.
Software: While I have run into some software issues (program wont launch) --- after testing the program in a WinXP virtual machine - they were not applications I would use (am very picky), nor pay the price that was required for them.
Otherwise, everything that I use on a regular basis works just fine,
- The slew of freeware utilities/accessories that I use; some dating back to Win98, all work with their current versions.
- (current versions): Opera, TC, EmEditor, Notepad2, Ted's Notepad, Codelobster PHP Editor, Putty, IrfanView, XNView, Media Player Classic, locate32, etc.
- (older versions): VMWare 5.5.9, VirtualBox 1.5.6, WinAmp 2.95 (I believe 5 will work, but it's in no way better than the classic version).
Dating back to Win98, I used Tiny Personal Firewall, which became Kerio Personal Firewall, which became Sunbelt Personal Firewall -- when I had switched to Win2K. I even have licenses for SPF and vipre, and I haven't even bothered to install either this time around.
The productivity losses from filtering all internet traffic and all file access through a software bottleneck isn't worth it. If something bad happens that can't be resolved in SafeMode or Recovery Console, then I reinstall --- and within the hour my system is back and running. My OS is kept separate from my UserData and Program Installs. Most programs will rebuild their registry requirements upon launch - they don't actually need to be installed.
In fact, the only reasons I've ever reinstalled my system were due to hosing by Symantec and to get a clean registry/system (I slipstream all the required patches into the OS System Install Disk).
System Requirements: Out of the box Win2K minimum requirements are 128MB of RAM, recommended 256MB --- vs --- WinXP's 256MB min; recommended 512MB. Win2K runs less than half as many services and background processes than WinXP.
System Uptime: Under Win98, I usually got 3-5 weeks uptime. Under Win2K, I generally only reboot when required to for Application Installs. Prior to physically moving my machine my last uptime was 3 months or so.
System Stability: Periodically will run into graphic stack corruption that locks up the system, or whitescreens - lose toolbars, etc. This occurs 2 or 3 times a year maybe. Most times I can resolve that (if I am able to get the task manager running) by closing everything down --- otherwise reboot. I haven't had a BSOD since I got rid of that piece of crap (NVIDIA based) ASUS K8N-E DELUXE NFORCE 2.5 motherboard --- replaced a $160 Mobo with a $20 one (ASRock K8Upgrade-NF3 Socket 754) and all of my system problems went away.
Hardware Support: My sony mp3 player couldn't do playlists without Windows Media Player 10/11. I didn't care much, but when I had to replace it due to an ocean accident, I got a fully functional Sansa Fuze 8GB (with a micro-SDHC expansion slot). Sony: $200, 8GB ... Sansa $40, 8GB + $25: 16GB micro-SDHC card.
Open Source: No, but that doesn't stop people from hacking it to make it do what they want. Granted Open Source would be better
User Friendliness: Say what you want, but it is easier to setup Network cards, etc in Network Neighborhood under Win2K than WinXP's legoland interface. And Win7's interface is even worse, most of the stuff you need is hidden behind a pretty display and GUI that doesn't tell you much of anything at all when things don't "just work".
Pleasant Visual Design: No. And I like it like that.
Technical Capabilities: What can't I do with this OS? I can't run some of Microsoft's latest software and the odd .DotNet 3.0/4.0 app. But neither can karlchen under linux
Total Range of Software: As much or more than is available for linux. And almost all of the software actually has professionally written documentation. Note, many apps written for linux will also run/compile for Windows. And many Windows apps will run (with Wine) under linux.
Scripting Support: AutoHotkey, AutoIT, PowerPro, Dos Batch, Linux Bash. I can run Cygwin shell under win2K and get linux in a box when I need it

without the overhead of a virtual machine.
Note, as I stated above: I will be upgrading to Win7. As I don't expect my newest hardware purchases to work properly under Win2K, and software compatibility is going to get worse over time as more devs switch to MS Visual C 2010.
But this poll is what is your favorite. Not what is the latest oooh shiny. I've used WinXP, Vista, Win7. People that claim "productivity gains" with the latter... are likely Explorer users - as Explorer under Vista/Win7 blows Win2K and WinXP's out of the water. For myself, Total Commander is my program launcher, and system interface along with AHK and command prompts for the most part. Win7 isn't going to make that better. The UAC system will technically be more secure, but it certainly wont be more streamlined than Win2K was.