First off, that is a good gift for a kayaker or rafter to receive.
I have the original hydro skin long pants and the newer version without the extra padding on the knee area. Since I am over the hill and beat up, I wish NRS had kept the knee padding.
I also have and used the neoprene NRS long pants.
The neoprene version is by far the warmer setup and gives the most protection if your luck / skill set runs out on a gnarly rocky swim. Having said that, I rarely use my neoprene pants version.
I wear the hydro skin pants quite a bit. Especially in the summer on the ARK at Buena Vista CO and on down stream. They do add some warmth and padding and not nearly as clammy as the neoprene version. Wet hydro skin does cool down if the wind blows and I am rowing, I have put on a pair of splash pants over the hydro skin and that helps the warmth factor a bit.
Bottom line for comfort and some protection, go Hydro skin
For lot more warmth and protection but real clammy damp feel, go neoprene.
Don't get rid of the wet suit just yet, but I bet that hydro skin becomes a favorite when the air is warm but the water cold and you want some just in case protection.