Jools said:
I think your requirements are reasonable, but not indispensable. I think a great, or even epic, RPG can be made even with a limited use of the elements you mentioned. That said, I cannot come up with a definition of RPG. Every time I come up with one, there are always a few games that -are- RPG's but don't fit into the definition. Therefore, I give up. :D
Since we are having a reasonable conversation, let me present my opinion a bit further, spreading out my points into three instead of two:
1) A character development system allowing Leveling and/or XP/skill points (Vampires!)
2) A nonlinear story splattered with Choices + Consequences
3) A flexible game mechanic that provides a varied gameplay according to a role you can choose to play. This need not be hard coded but a skill/feat distribution system that forces to choose only a few skills/feats can practically make you specialize or suffer gimping.
I think these are common features of all so called RPGs. 1 AND 2 are necessary elements, whether there is only one character to play or customization is available. The third is the cherry. Oblivion/Fallout 3 are spoiled because of the lack of the third in my opinion. Deus Ex specifically did a great job (for its time) on the second part, even when it wasn't a hard non-linear game (3 end choices unaffected by the rest of the game).
I am not against a single character RPG at all. I just feel that the element of customization makes the game worth its while
Also, I think that combat should be entertaining: Meaning that it should be tactical and intelligent; loot should be scarce ( no +10 swords of pink hippopotami) and magic should be limited (no spell of eternal doom) so that it does not become trivialized. But that's just my opinion man.