Put up some shade cloth to save the last few living needles, I don't think you can do much more. Next time, don't transplant in mid summer

Other than the shade, should I water it a lot?

Why doesn't anyone tell us where they are located?!

It's not like we're gonna come over to visit. ;)

Otherwise, like hug says, transplanting in midsummer is generally not recommended. But yes, it does depend some on where you are and what the Summer has been like. I myself HAVE transplanted here in NJ/Zone 7 this summer as it has been so WET. Previous two summers though were drought-ridden and hot.

Generally, they like water and a HEALTHY Metasequoia could not be overwatered in the growing season.

I would LET IT GO for the season. It will probably come back in the Spring (if still alive at this point).

Scratch just beneath the bark and see if you see green plant tissue. If you do, IT'S ALIVE!

It's in zone 8, since it was transplanted it's been raining heavily almost every day.

Victor, it can still be transplant shock. It's a deciduous tree so might just be shutting down for the season (while it roots during the Autumn months into Winter btw). Do the scratch test for vitality; then, if it's green, just forget about it. Should releaf in the Spring.

DO NOT FEED IT!

Also, I notice you removed some soil from around the tree. Do you think you might have planted it too deeply?

The highest root is at surface level, so I don't think it's deep. I removed the soil to check if the roots were ok, I filled it in shortly after.

I don't think it's too deep either. Was the soil amended?

I did add some fertilizer, should I remove it?

I should mention it was planted too deep at its previous location so some of the roots seem to be circling the tree. The location was very dry, so many of the leaves were brown before the transplantation. It stood there for 5 years without growing at all.

"I did add some fertilizer, should I remove it?"

How would you remove fertilizer? Do tell.

You can flush it with a lot of water to remove the fertilizer.

"I should mention it was planted too deep at its previous location so some of the roots seem to be circling the tree"

So did you straighten them all out and point them in the proper direction when you moved it? Doesn't look to me like you dug a hole wide enough to do that.

If you dug as tiny a hole as possible just to be able to cram in a distressed tree with circling roots and then added fertilizer to that very small volume of soil, then of course it is going to do poorly and probably die.

If it was me and I wanted to save it I would 1) dig it out and enlarge the width of the planting hole enough that I could straighten out all of the roots, 2) try and remove some fertilizer infested soil and mix whatever is left really well with that you dig when expanding the hole, 3) replant it making sure it wasn't too deep even after it settles, 4) remove all that grass surrounding it and mulch it properly, 5) build a temporary shade structure out of fence stakes and sheets or whatever else I could rig until it establishes, then 6) hold my breath until next spring which is when you will know whether all this worked or not.

Looks almost like fall color, albeit a pale version thereof.

When I have seen them defoliate they do that.