What if there were some cool physics/movement effects with water? For example, if you hit water at reasonably parallel angle going >1000ups, maybe you could "skim" over it? A way this could work is that ground friction on water is proportional (to some factor) to your speed when you hit the water material. Once you fall beneath like 750ups, you sink into the water like normal. That might be a nice way to add some uniqueness to Reflex's movement physics without necessarily changing the physics/mechanics itself.
This could result in some cool map designs: for example, making an area with water but a really low ceiling (just above head) so you cannot strafejump across the water. So you'd need to be going fast enough to "skim" through (without strafejumping/bhopping) over the top of the water before the water's friction reduces your speed so much that you sink into it!
Could be very interesting for race mode but also imagine CTF maps where you could take a "risky" route to escape across water. Or even a duel map!
EDIT: Oh yea, also: SLICK PLEASE!