One of the big advantages of WTP is the increase in personal space, having even slim neighbours overflowing the armrest. The fact you have a maximum of 1 person to climb over or have climbing over you is another major bonus on long haul.
The legroom is a second concern, although the lack of jabbing in the back (people in WTP tend to use the handset rather than the touchscreen), and people using your seat to lever themselves out are big benefits.
The seat, at least in old WTP (not managed to get new WTP yet), is far more comfortable than the seats on the A321 mid haul, which I find unusable after about 3 hours without medication. I've been fortunate enough to avoid WT in anything longer than TLV for the last 2 years, however I did fly in economy from Delhi to Singapore on Singapore Airlines recently, and again about 3 hours in, I started having real problems with the seat.