From someone who travelled on them regularly most of their lives, save for a few years under National Express East Anglia, they were well and truly a breath of fresh air compared to what they replaced, especially the 312s and the 321s.
The 360s are quieter, give a far better ride quality and have excellent air conditioning compared to what they replaced. The seats are also far better than the poorly angled seats on the 321s that are not natural for a tall person. They were easily too powerful for the allocations that they were on and could, as has been said upthread, be running 10 minutes or so late and easily make that up. E
Their build quality always was excellent with everything from the passenger information systems to the fittings on the train. Very few rattles even at tops peed and they always gave a nice quiet ride. I have only been on one that failed in the time that I have been on them and on that occasion it did not appear anything really dramatic. I've seen the odd door out of action but that was very rare and of course someone flooding the toilet every now and then.
Sadly especially in later years in Greater Anglia they were unloved inside and lacked proper cleaning and care and started to look very tired. It looked totally like a TOC who had decided to merely focus on the short term as they knew the stock was leaving. So it does not surprise me that there have been some issues with them on the new services since they have been unloved somewhat for a while. I know that some people i were disappointed as well when those units won a golden spanner that GA seemed disinterested in actually telling anyone it or mentioning the fact.
I think we have to look at the fact that maintenance was really let go with maintenance of stock leaving GA.. They went from 84,000 MTIN to 17,900 within a year. Class 379s went from 62,400 to 38,200, the 317s went from 12,500 to approx 10,000, the 321s from 28,500 to 19,500. No wonder there were so many short forms on the period the 2020 golden spanners covered.
Sadly I never got a chance to travel on one of them in the months before they left thanks to COVID, but I hope to catch one on EMR in the future. They really transformed the routes they operated on when they came into service and were a solid, modern project with build quality that you rarely see. I really think the whole Desiro family with the 350/444/450 cousins was the best EMU platform of it's time. Time and time again it's been top of the league tables and the build quality has always put Bombardier to shame.
Also kudos has to go with both First and Stagecoach for having the boldness to go down the road they did with them in terms of the kind of full maintenance contract they were on. Siemens were new to the full train build market in the UK, but they worked really well with these two groups and anyone I speak to about them, says that they were a massive breath of fresh air compared to what both Stagecoach and First had been dealing with in relation to the Alstom fleets they previously procured.
As for the Renatus 321s, they have better seats and are more modern inside and have plug sockets (if you are lucky) compared to the standard 321s. There. I named three good things. There are many other bad things about them that a list would be as long as my arm and overall they are not in the same league as the 360s, and apart from the three things I mentioned earlier, there are many aspects which I'd prefer a 321 to a Renatus 321.