Took a trip on a 331 from Ilkley to Leeds 2 weeks ago, and I was pretty impressed. There definitely was a nice "New Train smell" as you walk on, and the door opening chime wasn't as atrocious as the 322 sound (It feels like somebody is screaming into my ear with the 322 chime and you quickly develop a headache!) It does seem like a very table based train from an initial glance. One issue I noted was the constant humming sound from above; people have noted it before on the 195 thread as well. I found it to be a bit jolty in places, sometimes it would be as bad as a 80x in my opinion.
There is very little leg room, so I had problems with having my bag next to my legs, ultimately opting to put it under the seat itself. There also isn't very much space for large bags (for say the climbing mat I had with me) but that isn't the end of the world as most Northern units don't have a huge amount of space for large bags other than the 158 and even the 156. The seats weren't that bad for the most part, however I think I would opt to take a 333 seat over the flat cloth, even with the 2 + 3 seating arrangement.
Overall in my opinion, I think that they are good units that I would be happy to travel on again in the future. My only concern is that they don't appear to have too much standing space, with the only noted space being by the door area. Between the choice of a class 333, I think I would just barely pick a 331 due to the nicer interior. I think I would give it an 8/10.
