This article contains speculation, information which has not been confirmed by a reliable source. The game is still in development, and all information is subject to change.
What is known of the gameplay mechanics of Firefall thus far are just speculations derived from analysis of videos and developer comments on the Firefall forums.
Firefall is a team-based third-person/first-person shooter in a sci-fi setting with all that this implies. There will be RPG-elements, such as leveling and item-collection, as well as several tiers of item levels, but how these factors will affect gameplay is not certain as of yet. Every player will have access to "Battleframes", which effectively determine your class / combat role, that can be upgraded and customized by the players in-game.
It seems that every player will have access to two weapons in each load-out, one primary and one secondary, with the primary having an unlimited supply of ammunition while the secondary has a limited supply. Discussions are raging as to whether players will be able to dual-wield certain weapon-types, as seen in this CG-trailer, but it seems unlikely that a similar system will be implemented due to restrictions found in the battleframes' load-out screen as seen in the gameplay video.
Battleframes will decide the characters' role will be in the groups. Thus far the Medic and Assault battleframes have been announced, but there is the possibility of an engineering class, based on the female character seen in the CG-trailer.
Players will be given access to multiple forms of transport , ranging from jetboots, to dropships. Speculation concerning the piloting of these dropships and the existence of other vehicles, such as motorbike-lookalikes and tanks, are yet to be confirmed, although heavier forms of player-operated vehicles seem to be present in this recruitment video.
Character level seems to primarily determine access to better armor and equipment. The 'Forge' screen in the gameplay video shows numbered symbols next to some pieces of equipment. Current speculation holds that the symbols are Battleframe requirements (Assault having the lightning bolt, and Medic having the 'red cross' plus sign) and the numbers are level requirements.