The thing about the demo was the map. The map itself was tiny, and this itself promotes a certain playstyle that differs from the norm. Plus we were restricted in the weapon choices (ie: no smg's) meant that players were generally better of focusing on close range attacks with weapons like the shotgun. Something which many complained was OP when its not as proven by the fact it was thoroughly playtested in Crysis. Same thing for melee, as the tight confines of the map made shooting much less of a focus due to always being on close proximity to the enemy.
Before we start really thinking of whats needing improvement, we need a larger map with more weapon variations. This will allow us all to see what areas of the gameplay are lacking and which are fine. Always keep in mind that everyone has a particular playstyle they prefer. Be it camping, run n gun, melee, stealth etc. There will always be disagrements on what is in need of change, so the best course of action is to play the full game and see whats what in your opinion. If we reach a concensus on a subject that should be the devs focus.
It should also be noted that the leaked version is from before the demo, so its melee system is out of date. And the melee system itself will change from that seen in Demo on 360. We just have to wait and see what the devs decide is a happy medium between the two.