I'll take that challenge, as a BAEC GCH. I have flown from T1 several times since the change, to TLV and LYS, and quite happy with it. Some advantages compared to T5;

1. Shorter journey on Heathrow Express
2. Quicker security, and working/enforced Fasttrack - last time I had checked in luggage, passed security and in lounge just a minute or two after Heathrow Express had arrived in T5..
3. Very pleasant and attentive staff in lounge (ex-BMI I think, nicer than T5 IMO)
4. Better newspaper/magazine selection (replenished more frequently I think) than in T5
5. Better kosher food (OK, I know that is personal benefit)
6. Lounge is closer to gates commonly used (5, 76,78) than most gates in T5 - and even 20's pier is no further than A gates in T5 would be, less time than train to B/C
7. Better showers in lounge, with no 'gurgling'
8. Lounge never seems full up
9. Flights are called in the lounge as there are so few of them - so no waiting around the gate or wondering when to leave

I agree there are disadvantages - connections poor (unless you connect LYS-LHR-TLV as I do!), drinks not as good in lounge etc - but overall I find that the comparison is not completely one-sided....