I just flew on a refurb 319 in F and a 320 in Y. It's probably valid to assume that the interior of the 321 will be the same. Here are my findings and impressions.

In F:
The seats are comfortable, there was adequate leg room and under seat storage. The headrests raise. The tray table is unsupported at one end so they'll start to sag. The tray tables are on the small side. The recline is not like the existing 320's and there's more leg room so you don't have the problem of loosing all of your space. The aisle armrest raises. The pivot bins overhead provide much better storage space. Despite the diagrams, people didn't turn their bags up but there was still adequate space (flights weren't full). Mood lighting. The light control and air vent are tough to reach from the aisle seat. The F lav is large enough. I don't use the IFE so I can't comment about the services.

In Y C+:
The seats are comfortable, headrests raise, aisle armrests raise, adequate leg room. Underseat storage for the middle seat in Row 11 is limited by an IFE box (I didn't check other rows) . The aisle is narrower to accommodate the wider seats. Pivot for overhead storage. The lavs are TINY. They'll be a problem for large people. Most aisle pax won't be able to get to light / air vent without leaning over center seat pax.

321 engines are the same as the 319/320 and I believe the hydraulics are as well, so you'll have the same noises. The new 319 was a comfortable 3+ hour ride SLC-MSY (with noise cancelling headphones and my own music) and I imagine that the 321 will be fine for those routes as well.