I've flown once so far, and have 3 more EWR sectors in the next few months. 0 JFK. I never thought I'd use EWR to this extent but so far it's easier to get D and I fare tix to/from EWR than JFK, CX890 is an hour earlier than CX846, and it seems like EWR-midtown drive is at worst the same, but much likely faster into downtown or midtown. I'm not from NY so maybe this is wrong but that's how it seems to me. The downside is I can't buy J and use miles to upgrade to F, but that's really not the end of the world.
The other thing EWR enables for me I didn't realize was meetings in Philadelphia are easier. I can shave off 30-60 minutes of transport time by going ex-EWR instead of having to drive out to JFK. I'm ending two upcoming USA trips ex-EWR, whereas before I probably would've either gone ex-JFK or made the trip so that I ended in California and went ex-SFO or ex-LAX. EWR is a nice option.
My main concern about EWR is if a plane goes tech at EWR. I imagine it will suck given there's only one flight a day. Someone posted something like that the first week EWR was launched didn't sound fun. At least at JFK there is so much metal CX has some flexibility.