I've noticed Arriva have been doing really well recently, though I noticed two things whilst travelling over the last week.
I caught a service from Newport (ex Carmarthen) to Shrewsbury (continuing to Manchester) last Tuesday, my train was about 8 late from Newport but was nearly 30 minutes late by Craven Arms/Church Stretton/Shrewsbury and I almost missed the Cambrian & Cambrian Coast service from Shrewsbury! I always try to have at least half an hour to change and I'm glad I did this as if I had taken the recommended Holyhead train, I would have missed it, had to wait nearly two hours and then changed at Machynlleth as well as get replacement bus transport at Barmouth.
The trains have also been delayed on the coast line in the last week but this is understandable, particularly because the line has just re-opened to Harlech. Trains have been hanging around at Tywyn for over 15 minutes waiting for another train to pass, and at some stations, the departure board does not update any further delays and just wipes the train off when it's still over 5 minutes away. This isn't really an issue though due to the relatively few services. Another thing is that some stations along the Cambrian coast only list the train as going as far as Machynlleth, and then you get on there are reservations to stations like Wolverhampton. Obviously it forms the front half of the Birmingham services, but some of the stations said it was going to Birmingham New Street, some were saying Machynlleth and the onboard displays were saying it was going to Birmingham International, and if you're doing a long journey, none of these show up on the national rail website. Slightly confusing!!
Everything else has been super though, the staff and the service and I have been really impressed recently. I even saw a 2x 175 operating together on Bank Holiday Monday!