He's capable of soaking up enormous amounts of enemy fire. Much like the marine from Quake , really. He also, like other Nod mutants, heals when in tiberium fields. For the GDI, there's a commando with a railgun that can destroy many targets at once. He also carries the familiar C4 explosives for blowing up buildings.
New structures make an appearance too, although the traditional base facilities remain unchanged.
Power plants are needed to supply the base with electricity, and silos hold the precious tiberium until you have a chance to spend it. But this time GDI has the option to upgrade certain buildings to increase their capacity or add extra abilities. Sadly there is no provision for placing multiple weapons on one turret, but the turrets do slot neatly into any concrete walls you choose to build. Both sides get various types of high-tech laser fencing, impenetrable unless the power is cut off. Westwood really deserve congratulations in this respect.