Been playing this since the promo dropped; it feels pretty decent. Original goal was to make a deck that used no legendaries and could hold its own. Ended up with a 13-7 win-loss ratio, but I expect that'll drop considerably once people become more familiar with the card.
Water Conjuring is an absolute MVP, as is Nahid's Faithful. Using Piercing Grief or Dark Wisp into Nahid's Faithful early is pretty good for staying in the game until your gameplan comes online, and post-Judgement, it's a very easy to cast lifesteal unit to keep you ahead on life while you rebuild, if you didn't get a waystone gate down or your opponent kills your giant.
Shattered Hopes feels underwhelming, but it's a cheap Decimate card and it proactively deals with a lot of the bullshit in the meta right now (e.g. Grodov's Stranger). This is probably the #1 card I'd cut. It is cute against other Lastlight Judgement decks, as long as you do it while Judgement costs 6 or more.
Getting Lastlight Judgement down to 0 cost before using it the first time is pretty key unless you absolutely have to use it earlier. Being able to throw down another one post-Judgement if your opponent starts rebuilding faster is very key.
Don't fall into the trap of trying to Judgement too early, or in trying to keep Bottled Storm or Waystone Gate around for Judgement if you can use it earlier and are in a good board position. Sometimes you don't need to Judgement to win; Soulflame Rider makes a very solid threat and sometimes you can get it down by turn 2 or 3, and it's often possible to Invoke something that can win you the game from Water Conjuring.
A cute trick is to hold Reap in hand until you're ready to play Lastlight Judgement, and play it immediately before. You can determine if your opponent is holding anything that could interact with judgement - everything that could respond to Judgement can also respond to Reap, so if there's no pause when you Reap, you're definitely in the clear. Nothing sucks worse than having your opponent respond by giving themselves / their board aegis.
Overall, fun card. I don't think it's top tier by any stretch but if you're looking for a fun deck to mess around with and want something that's super cheap to make, this is it.
Edit: Replaced Lastlight Infusion with Lastlight Judgement now that it's on the site.