Okay, you're looking at SH4 out of the box. Have you looked at any of the environmental mods? I guess none of you were around when SH3 was new. Play SH3 with no mods for awhile. You'll see a huge difference. As for graphics comparisons, here are a couple of similar shots from both.
SH3 with GWX 2.1 and IABL's new T2 model:
And SH4 with no mods except WClear's environment:
SH4's graphic engine is a definite improvement, and once the different modders have put their touch on the Atlantic side, it's going to be even better. I love SH3, but I think in another year or two it will be forgotten, as SH4 is the same game with better crew management, better campaign management, better loading times and better graphics.
For now, stick with it, but don't knock the future. It can only get better.