While I didn't main purfier during the beta, I'm quite familiar with its root abilities and tree. Although I plan on utilizing mostly warden spells in my final pve healing build, I'll have actually spent more points in the purifier tree.
Their base crit bonus talent is incredibly useful in conjunction with either of the other trees to help proc other talents, and they get a 31 point talent to help them deal with the potential overheal of crits. Their pushback resistance is very good and coupled with their shield means you can cast freely through being attacked (quite nice in pvp). They've got some nice emergency tools as well.