I'd have to say I prefer the gfx in Turrican 2 compared to 1. The originals graphics look a bit like an 8bit pixeller's first go at 16bit to me. I also prefer the way that when you 360 the gun in Turrican 2, the whole character rotates, rather than just the fire itself. Also, the status bar in the original is rather hideous.
I can't comment on the gameplay as I haven't really played the original for any decent amount of time.