I think the Shadow is cool but it doesn't have the same all-around draw that White Water has and feels a little sterile in comparison. The theme, art, progressive music, and ramp madness of White Water all intergrate well. That being said, it's hard to beat Shadow when you look at the value. I kind of think Shadow is the better long-term buy, even though White Water would be easier to sell if you don't tend to hold on to games.
Also, if you find White Water "easy" then you've got it set up wrong. First, ball save? Seriously? Why not set it on 15 balls? Why not take the glass off and use your finger to hit the microswitches? Psshhhh. What's next, ball save on Taxi? The home ROM is great but fuck the ball save. Second, open up that right outlane and see what happens to your scores. Third, if your lost mine has been castrated to hand the ball to you on a silver platter then no wonder the game is so "easy." Lastly, the old school arcade sounds on games from that era are bad-ass.