RAMburger: Oh yes I certainly have played them. The original is still one of my all time favorites (Bioware engine be damned)! In fact, outside of combat mechanics and that engine's limitations I still prefer its design next to TW2.
One question on TW3 though, how much is affected with an imported save from TW2? I have one with both killing and sparing Letho, but not sure if the game lets you choose which save to implement.
Thanks,
I commend you for having fine taste :) The first Witcher is shamefully underappreciated imho.
Regarding your question, there are a couple of things to note:
The game has a mechanic that will allow you to "simulate" a couple of choices from the last game (Letho being one of them) if you don't have an appropriate save at hand. This works fairly well and is implemented nicely (it happens after the prologue and is implemented into the story, you can't really miss it, but it's necessary to check "simulate save" whilst starting a new game).
You can also import your save from the last game (it will add a couple of odds and ends from TW2 you won't see otherwise - a certain optional tattoo, for example). You must use a save from the very end though. IIRC there's one autosave the game creates after the Letho bit, any earlier save will mean the choice isn't implemented correctly.
The sad news: it makes hardly any difference for the story, mostly it adds a line of dialogue or two here and there, the big choices (Saskia, Iorveth vs Roche) aren't really reflected in any meaningful way. Letho alive adds an enjoyable quest you won't get otherwise, though.