Halo for the pc is almost a special edition of sorts. Its well worth buying if you have not played through the whole game and do not ahve an xbox or want to play it online. Its almost a special edition of sorts with some new content to boost it forward.
I am not going to go into the details since you can just read my review for the original xbox title. But heres a shakedown on what makes this version different.
The PC nowadays is capable of making games look much better than they ever could on a console system, so for those with strong computers a better visual experience is now possible.
The gameplay will vary depending on if you like PC FPSs. It could take a while to get used to not using an xbox controller but its not a huge deal.
The Sound is pretty much the same, but a PC can make the sound better with the right audio hardware i suppose.
The biggest difference is in the multiplayer. Now you can select new weapons and new maps to play on. You can play in a LAN, or you can play oline, this is something fans of the orignal were disappointed about when it came out for the xbox. There was no online, well now there is. I have not had a chance to actually play online but i played on the maps and used some of the weapons and they are all real cool. Banshees are now available on all maps as well.
I have played both versions of the campaign and find them both to be very satisfying. However I would prefer the xbox gameplay to the computer if only because of using the controller. However the computer's new features may make it a better buy for those who like multiplayer games a whole lot.
Overall its essentially the same. But the new goodies can make it all worth it for those who like to play with friends, ESPECIALLY if you have no xbox, then its a good buy.