Haven't sampled 745 first class, but the standard class in definitely much better than the Mk3, which was quite cramped with fixed armrests. From what I've seen the first class will be better than the GA Mk3 first class too.
240V and USB power at every seat pair, comfy seat, nice open airy ambience but with the glass partition doors giving a cosy "compartment" feel, quiet and a very smooth ride. What's not to like?
InterCity 70 seats are awful, worse than Fainsa Sophias. However the First Class seats on those Mk3s (IC80?) were quite nice. So I'm going FLIRT in Standard but Mk3 in 1st.
I didn't mind the IC70's once I'd fought my way over the armrest and sat down, but I still prefer the 745.
The first class seats are the original IC80 type, albeit with new fabric. They were also used in the APT prototype of the same era. The recline mechanism was broken on many of them so the Abellio refurbishment simply fixed them in the laid back position and covered up the adjust button that was on the armrest.
Back on topic, I miss the old trains but purely for nostalgic reasons. There is no denying the Stadlers are a far superior train, as is to be expected with a forty year newer design.
Ah! That explains the biggest issue I had with the GA 1st class! It was impossible to work comfortably because the seat was so laid back - you either needed to have Gadget Arms or sit hunched forward which became uncomfortable very quickly. I always thought it was weird the seats were so laid back. They lost loads of first class fares from me and others as I used to just bag a table seat in standard as that was so much more practical for getting work done.
If you just wanted to lol about and gaze out of the window there were comfy enough though!
Similarly, I miss the Mk3s for nostalgic reasons. There is the "je ne sais quot" about a loco-hauled rake pulling up, the big heavy slam doors and the THUMP on every departure from Liverpool Street as the 90 pushed up into the rake. But I prefer the 745 experience and they are an absolutely superb train to travel on.