They are claiming some significant improvements. Here's something from the executive producer:
"Getting our gameplay up to native 1080p meant increasing all of our texture resolutions by over 4x so the details and nuances can be seen in their full glory. However, it’s subtleties like our subsurface scattering technology — how we manage realistic lighting effects through solid/semi-solid matter — that we’re so proud of..."
"...trees whip in the wind; even cloth moves courtesy of new, more sophisticated physics modeling. Weather effects lash the island with unprecedented levels of venom, and rain particles are dynamically lit as they slice through piercing searchlights. The in-game cast has also enjoyed an upgrade — characters and enemies alike have been enhanced visually, while in-game destructibility has been given additional refinement ...."
"However, as always, it’s Lara who’s the star of the show. As such, one of our boldest changes was to handcraft an all new, even more realistic head and face model for her, taking advantage of the increased power of PS4. This is our first glimpse of our next-generation Lara. We also drastically improved shader and lighting effects, adding dynamic sweat, mud, and even blood for a new level of visual acuity that reacts on Lara in different situations. Objects on Lara’s person like her climbing axe or arrows now independently react to her movements and sway or jostle with an obsessive eye for detail..."
"Lara’s hair now benefits from TressFX technology — her hair strands are independently simulated and interact with environmental effects, as well as react to her every movement, delivering unprecedented, lifelike motion. This all-new Lara is Crystal’s first steps towards the future. It’s a promising, compelling beginning."
http://blog.us.playstation.com/2013/12/07/tomb-raider-definitive-edition-detailed-on-ps4-january-28th/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed: PSBlog (PlayStation.Blog)
