These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Bittersweet Ending: Our heroes have saved reality!... or at least, a tiny fragment of it... Almost everything and everyone that ever existed is not just dead but erased from all memory. note (and they got to see their end coming inescapably toward them, so all those googol plexes worth of people died in sheer terror). And the coming months will show that even the survivors have been drastically altered by the experience, mostly becoming more violent and depressed, and have no memory of ever having been otherwise, let alone of what caused it. So... yay?
Fountain of Memes: Pick a cover. Any cover. They'll all become iconic (though probably the #1 is Superman holding a dead Supergirl.)
Jerkass Woobie: The Psycho Pirate is a sicko and a coward yet it is easy to pity him when he goes mad from fear.
Narm: "It's not fair. She shouldn't have died for me. Where is he? The Anti-Monitor. I... I want to kill him for this!" It's the horrible punctuation that really sells it.
Wolfman always has embraced the natural cheese that comes with the comic book medium, but here, simply the amount of characters present, and his need to have each one's name spoken aloud by another character, along with multiple characters thinking repeatedly about what their powers enable them to do, ramps up the narm factor exponentially.
That one panel where the Anti-Monitor appears to be air-guitaring.
Uncle Sam's speech to the gathered heroes is really hard to take seriously. Of course, that might have been the point, as right afterwards the line "What a cornball!" is said about him.
When the Challengers of the Unknown realize the darkness in the sky is composed of millions of shadow demons, they're naturally shocked. Unfortunately, June expresses that shock by saying each of her teammate's names all in a row. Seems very unnatural.
Did poor Wally really have to say twelve little no's followed by one big one when he sees Barry Allen's empty costume?
Tearjerker: Even if you thought pre-Crisis DC was a mess, it's still pretty upsetting to see several different alternate continuities come to an end in a single story.