At first I might not actually notice, I'm not sure. I would see with much higher clarity for example, and might break something with my Augmented strength, like Adam Jensen does in the Deus Ex: Human Revolution trailer. He reaches for a glass of what looks like Jack Daniel's whiskey, but it starts to break in his hand. I'd still seem exactly like myself in my 'defult' Human form, although I would also be able to change my appearance in Human form, like color, height, weight, gender, and voice. I would not abuse that. Several immediate advantages I could have would be a lack of the following; sweating, skin cell shedding, pimples, sunburn, and scarring. I would have full control over where and how my hair grows, and would keep it to my scalp and maybe face only. No other body hair at all. I'd also be immune to diseases, aging, and would be pretty damn hard to kill. I'd be pretty much like a Terminator. :P
I would then get to the really awesome part, and experiement with my new shapeshifting powers in private. I'm not sure if I would take a non-Human form in public, but I would like to just so my powers wouldn't go to waste. I would finally get to learn if being a cold-blooded Reptile really is as great as I think it would be. Also thanks to my Augmented strength and durability, (Not to mention my vision. XP) I'd be able to take a large Insectoid form without needing more Oxygen. And since I would be able to manipulate my own shape in ANY way I want, and not just simply pick from a library of quick forms, I'd be able to become any sort of crazy Chimera I'd want to be if I wanted.
I know! I could take my own arm off, regenerate it, then give the severed Nanobiotechnologically/Mechanically-Augmented arm to some prosthetic designer or something so they could reverse engineer the technology, and perhaps make it possible for anyone to be whatever they want too. Perhaps I could spare an eye or larynx or some other parts too. DeNihil can disable sensations of pain.
Only potential 'problem' would be my new subtle Illuminati programming... but I wouldn't worry about that too much.