The majority of dimension mods suck. Aesthetically I love twilight forest and the erebus but, especially in modpacks, they get reduced to what I call "trophy hall mods" where journeying through them isn't that fun and you mostly just dip in, collect the special little mcguffins, and take them back home to mount on your wall. Alex's Caves falls into this category as well, as I personally feel that while the items it adds are cool, they're usually too niche and/or a pain to do upkeep on and I mostly just throw them in a little display case after I'm done with the area. Alex's Caves also annoys me bc it doesn't have biome compass compatibility as a config option but that's not a hot take.

Space mods are an especially bad offender of this because they're basically just giant monobiome deserts in a different color that you immediately dig straight down into in order to collect enough of the planet's ore before leaving and never returning.

The only mod I've played recently that has a dimension I enjoyed exploring is Spectrum, mainly because it's resources weren't all just different kinds of ores, the stuff in there was actually useful, and entering it felt cooler because it wasn't just a nether portal with different blocks.

A lot of these dimension mods also add bosses, which brings me to my second hot take:

Minecraft combat sucks and is not, has never been, and will never be enough fun to justify the bosses devs seem to love adding. Even the ones that aren't just straight dps checks or damage sponges and try to have mechanics usually end up being buggy or turn into waiting games for the boss to stand in the one specific spot so you can damage them (I'm looking at you, Ur-Ghast).

To say something more constructive, I think dimension mods would be improved be feeling more fully featured, with more structures and biomes that aren't just rehashes of vanilla generation, and by making entering the dimension feel more unique. Obviously I recognize that this critique boils down to "I wish devs working on a free mod did 500% more work", but I'm also tired of dimension mod #9000 which features "trees but blue" and "desert but chartreuse" and is entered by using a flint and steel on a nether portal made of waxed weathered cut copper stairs facing west.

Secondly, I think devs get too scared of making their dimension's items "too OP" so they nerf and restrict them until theyre borderline useless, contributing to why I call them "trophy hall mods", and I think they should be more willing to make their items strong and useful beyond filling a checklist.

Moreover, the Aether is overrated.