lol my mate and I were just talking about this today.
Pre prepared, 'coz I'm gonna use this thread as an excuse to dump ideas.
I think [Prototype] was a big waste. sure they made a good fun game, but the potential for a evolving game experience was hugely missed. We were talking about only being able to evolve up certain evolution trees and when you pick one, another was closed off, having real benefits and consequences for your choices.
For example, say you start with six choices for weapons (muscle arms, hammerfists, whipfist, claws, blade and a mass cannon), you can only choose three. As you upgrade them you unlock certain branches (say the whipfist having a bladed tip on the end or a bludgeon) where you can only pick one, forcing you to think about the advantages and disadvantages of having each upgrade. The you have two power classes, agility and power. there are skills in each
Agility has Running speed, jump hieght, gecko form (your climbing and perception), and winged form.
Power has general muscle strength, shell armour (a ball that you erect around yourself), armour plating and what I like to call Hulk armour form.
For normal powers (not forms) as you increase one, like running speed, by pouring xp into it, you slowly decrease your effectiveness at using Power normal abilities like shell armour, muscle and plating and vice versa. Conversely as you pour xp into one form (Which doesn't activate until you max out the xp bar) the ability to achieve other forms is weakened until you cam't get another form. It's designed so you choose wisely, as each form has advantages and disadvantages.
Gecko form has you transformsomewhat into a gecko-like cratue, with a large head with big eyes, finger and toe pads and a tail and you earn the abilities to use vision modes much better, climb and stick to surfaces with great speed, weaker frame, greatly increased speed and agility and a basic camo ability.
Hulk form basically makes you the rough size of the hulk, with huge, crab-like armour covering your body, making you impervious to bullets, massive strength, slow speed and turning and the most destructive forms of each weapon.
Finally, Winged form sees you sprouting massive wings from your back and taking to the skies, allowing you to fly and hover, giving you great speed, vicious talons and an aerial perspective of the battlefield.
Lastly but not least, there would be 6-player multiplayer, with free roam, co-op, deathmatch and team deathmatch, plus some others.