I was in G-POWS, Titan's 737-400 (formerly of British Airways) operating my Easyjet flight back a couple of days ago. So confining myself to the non-Easy elements:

The legroom was good, better than Easy or current BA - similar to pre-densified BA or maybe even better. The seats reclined (slightly), and there is a literature pocket up top of the seat and net pocket below which is a bit smaller than the BA seatback pocket. Good enough for small items but would struggle to contain a small laptop while you can easily park such in BA's seat for takeoff and landing. The aircraft was clearly old (ancient passenger service units, for example) but it was clean and everything worked. The seats were not as old as the aircraft, but also not young. The carpets looked recently replaced and were clean, very clean in fact. The crew were efficient, effective, and fairly friendly. The overhead bins were a bit smaller than the Airbus overhead bins but still held everyone's rollaboards. They're about as deep as BA Airbus bins but not quite as tall so there is a bit less opportunity to put things on your bag.

Looking outside, it was obvious how much closer to the ground everything is on a 737 compared to an A320-series.

The seat was not, I'm afraid, very comfortable to sit on although my knees were quite happy not to feel the seat in front. I feel it had already seen quite some length of service. The padding seemed quite limited so it was a bit hard both in the arse and the back (rather like an older Easyjet seat) whereas BA's seats are all still as comfortable as the manufacturer intended because they're all quite new. I think it was also about as narrow as an Easyjet seat, therefore a little narrower than a BA seat. So it was adequate for the shorter flight I was on, but I wouldn't want to sit on it to Athens or Stockholm. I was not in the exit row, which appeared to have even more generous legroom.

One oddity, in perception, is that I several times wondered where the fourth crew member had gone before realising that they did not have one. The aircraft has 146 seats so only three cabin crew are required, whereas BA (and Easyjet) have between 150 and 200 seats needing four crew.

Overall it was a reasonable experience and the legroom was welcome.