Um.. I guess it'd be pretty hard to "enlighten" you, after what you've written in your 2nd posting.
That's all your personal, very subjective opinion and I'm pretty sure I can't change anything about it. Of course, you can have your opinion, however, I still refer to it as "wrong" or at least "weird" in this case. From my personal point of view and from an objective one.
It's just that De Niro has one of the most impressive filmographies in the history of cinema. You may like only 5 films of his, but it'd be nice if you just left your subjective viewpoint, which seems to be characterized by dislike and unconcern for no apparent reason, for a moment, and tried to look at this from a neutral point of view. I mean, dismissing The Godfather: Part 2 seems already pretty ignorant and just saying that you dislike this or that film without giving any specific reasons, while basically all of them are regarded as classics, is a little weak as well.
I didn't really intend to go into detail with this posting, since I understand that this is a hopeless case of a "I have my opinion, you have yours" discussion anyway, but what the heck, here's a list of De Niro films that I consider to be masterpieces/classics.
Mean Streets (1973)
The Godfather: Part 2 (1974)
Taxi Driver (1976)
The Deer Hunter (1978)
Raging Bull (1980)
The King of Comedy (1983)
Once upon a time in America (1984)
Brazil (1985)
The Mission (1986)
Angel Heart (1987)
The Untouchables (1987)
Goodfellas (1990)
Awakenings (1990)
Casino (1995)
Heat (1995)
+ Jackie Brown (1997) and Wag the Dog (1997) and many more good ones.
Looks pretty impressive to me. No matter what your opinion on all of these is, you have to admit, that they have gained a certain status, most of them were regarded as masterpieces upon their release and as classics now, and I say, deservedly so. I don't think there are many actors who have a stronger (and more diverse) filmography and that many masterworks.
Also, note that not all of these are early 70s films, no matter how much you stretch that term. In fact, only 1-2 of them are.
Furthermore, I think that all of the listed films feature excellent or even monumental performances by De Niro. And there's definitely a great versatility (and creativity) in both the choice of films and the choice of roles. And yes, I didn't even mention the comedy roles (aside from the King of Comedy, if you want to call that one a comedy), those would broaden the spectrum even more.
To bring this to a conclusion I recommend this website:
http://www.thefab.net/movies/m02_de_niro.htm
If that's not a creative and diverse choice of films/roles, I can't think of many that actually are.