Actually, from what I have read and in my opinion, the most defining characteristic of the fifth generation aircraft was as follows,
1) All Aspect Stealth (the definition of this aspect was however different for all nations) even when armed - which might mean internal weapon bays.
2) Advance avionic features (upgrade from forth generation fighters), and again this is different for all countries, because of the different era and standard of development.
3) Low Probability of Intercept Radar (this work together with the all aspect stealth, one is exterior and one is radar)
4) highly integrated computer systems capable of networking with other elements within the theatre of war for situational awareness (okay, this system could also be loaded onto a fourth generation fighter too, as long as there are enough space in the aircraft, this can be loaded).
Of course of the above four, I am only seeing that the main difference of a fifth generation fighter to a fourth generation fighter actually differ only in that a fifth generation fighter had all aspect stealth incorporated into its features and that is about all. In actual fact, with the all aspect stealth even when armed, would also make carrying lesser missiles, size of the missiles, etc. If they hang those missiles outside, then they would lose their stealth.
