I wasn't really sure what I was going to play this league and I started as a Templar thinking I'd build a Guardian summoner. I ran Purifying Flame in the early campaign and found that I didn't want to stop using it, so I ended up in an Inquisitor crit build. It's been working pretty well in endgame (by my standards, being someone who doesn't look at guides or even Ninja for the most part any more), allowing me to beat some endgame bosses I hadn't been able to handle before.
It maps well but is fairly slow, I think, compared to something like Lightning Arrow. Great at flattening map bosses (because of the negated resistance from Inevitable Judgment) and serviceable for Guardians and others of that tier. Managed to beat Elder and Shaper but I'll have to have another go at Sirus. Haven't tried the Maven yet but it sounds like I should be able to handle that fight with some practice. Not sure if I have the DPS for Uber Elder.
Here are 4 videos to give an idea of the playstyle:
And here's the build: https://pobb.in/ZtHR1MMDweUm
I've been experimenting with replacing Sacred Flame Totem with a spell totem running Punishment, since currently I don't run a hex curse (Flammability has no effect due to my Ascendancy passives). I thought it would be much better for bossing, but so far it's been quite a bit worse. Although the Sacred Flame totems don't deal significant damage, they seem to draw fire and disrupt enemy attack patterns enough to be useful even in fights against Elder Guardians. So my damage uptime is much worse without them. I could also just hard cast Punishment, leaving 2 sockets open for something else.
I have something like 20 divine sitting around that I could throw at this build if there are some juicy upgrades to be had. Upgrading the staff and amulet (for another +3 spell levels total) seems like a good option but I didn't manage to find anything last time I looked, and the pickings are no doubt slimmer now.
I'm also probably going to start this build next league, so leveling and farming suggestions are also quite welcome. I was clearing essences with atlas investment as soon as I could get to them, and Harvest has been a steady flow of income, but I still haven't managed to figure out how to pull in more than a couple of divine per hour. Though actually I may be doing a bit more than that now that I'm dropping Maven invites frequently.