I actually kind of feel the opposite. I feels more like a realistic person to me at this point: his instability makes sense, his motives make sense, etc - whereas in the past he just wanted to be a crime kingpin despite already being a successful businessman and scientist.
I do agree that Warren Ellis wrote him beautifully in Thunderbolts, and I think that characterization will carry the character far into the future.
That being said, he is kinda boring now. It's not that his current storylines aren't interesting; it's more so that, before, the rivalry between him and Peter was so bitter and personal and intense. I've generally enjoyed the Norman stories we've gotten since those Thunderbolts issues, but yeah - something feels missing.
Honestly, I think the Norman-Harry relationship needs to become more front-and-center.
-Pav, whose "nostalgia" Osborn is post-CS / pre-reboot but has read plenty of older stuff...