First, the things I have not tried: new burner missions (nor older ones for that matter), French, pasting in fits, new notification system, any rebalanced ships or modules.
So what I have noticed so far?
Oceanus is pretty. I am not used to the new wormholes and wormhole backgrounds yet. That is, I still cannot just look at a wormhole and know where it goes (other than C1/C2). But I think this should be possible, so under that assumption it is good. I think I already can look at them and tell the small wormholes from the others. (Penny has a new post showing many of the new wormholes, similar to her older guide to wormhole appearances.)
I knew going into Oceanus that there would cooldown timers displayed. I sort of thought that meant cooldown for micro jump drives. And it does, I hope. (Have not checked.) But what it means for me is "cooldown" of cloak modules, which is very important. It's a real nuisance when you want to recloak to be sitting there hitting cloak every second since there is no way to know when to recloak. Now you can see it. Very nice. I am comically happy each time I go to recloak after firing probes. This will fade.
It does seem a bit daft to be so thankful to CCP for this. I mean, they should have done this years ago. Literally years. It is very helpful, and it is just client graphics; there is no server-side at all I should think. The client already had this info, which is why it could tell you how many seconds left via the pop-up message. All they had to do was display it.
One final thing I noticed today, when making the screenies for this. CCP seems to have fixed the bug where you get a delayed cloaking effect when you raise the system map before or when cloaking. (This bug was still there on the first two days of Oceanus. I noticed.) I have had a number of gasp-no! moments over this one. So I am glad it is fixed, assuming I am not just misunderstanding how it is triggered. [UPDATE: no, still not fixed. Come on, CCP.]