I didn't know you'd already played it. I fall under the assumption that most people playing it are doing so the first time. I've played it countless times (and I mean literally countless, maybe twenty or thirty plus times). I haven't, however, played it in about half a year, which is rare for me (I usually get a small break between playthroughs with another game or few, but never for this long), and intend to start on it again soon. It's my favorite game.
As for the shaders, for playing around, sure, they're fun. I've messed around with many plug-ins (software and hardware), settings, resolutions (high and low), filtering levels, shaders, etc. with this game.
For when I'm really playing it though, I have to have it look how it should, as natural as possible. When I first started playing it for the first time via emulation (I'd already played it many times over even before then), I settled with Pete's OpenGL 1 with a resolution of 1024x768, and the rest was about standard fare (filtering level of 4, etc.). Soon, the pixelation wore on what I remembered as crisp, smooth backgrounds, so I set out to make it natural. Lowering the resolution to 640x480, using a filtering level of 2, and screen smoothing, were what really helped. Once I got my 6800GS (heh, only had both a GeForce 4 MX440/Ti4200 before back in, what, 2004-2005?), I switched to Pete's OpenGL 2, and refined it a bit more to what I have now.
I should try and get some screenshots up myself, but I never took many (if any). 640x480 screenshots don't do any justice, so I never bothered. You have to see it in person on the screen. Otherwise, they'd probably just say "that's so small and blurry" and not understand (since the high resolutions and sharpness are one of emulation's features, but people don't understand that these aren't HD, and you can't get them as such no matter what you do).
Anyway, nice shots. Do share any others (shaders or not) that you happen to take.