From the perspective of a PMNW, platinum (may make diamond this year if I'm not careful), Hawaii resident:

Pros:
DL no longer charges me for wifi in the SC!
Gogo inflight wifi rollout has gone really well, congrats on that. ^
AVOD on domestic flights is an improvement.
Australia service, which I hope to someday use.
More bump opportunities and TATL/TPAC op-ups

Cons:
Lost CO as a partner (nonstops NYC-HNL and NYC-EDI)
Lost Mountain Dew, did not get Coke's "Vault" as a replacement.
Most DL call centers not quite up to the same standard as NW's fabled Chisholm.
Made miles easier to get, but harder to use.
Made SWUs easier to get, but harder to use.
American Express as an airline card. An airline that serves six continents pushing a card that is useless in so many places must require astounding amounts of cognitive dissonance. I'd love to send the people responsible on a weeklong tour of DL's African destinations, with no cash, just an AMEX.

Cons specific to retaining Hawaii-based customers:
Lost the upgrade certs NW would give Hawaii elites a few of, to make up for the fact that our EUA percentages would otherwise be super-low.
Messed up the codeshare relationship with HA, so I stopped getting miles for inter-island segments on HA. (I now book those through HA and credit to a HA account.)
Booking engine refuses to admit that there are flights (on HA) to ITO. NW's could, Expedia can, all their competition can... hint, guys.