It is sad that the designers put so much work into Candlestick Keep and Compound levels, yet they are universally the most hated levels among the playerbase (pretty sure the majority of players do NOT enjoy them as much as other levels). I have two points I'd like to highlight, why I think these levels are so reviled, and I hope the level designers take a gander here so they can keep it in mind as they design future levels.
1. Control. Players like being in control of the situation, and Grimalkins do the exact opposite: you can't kill them, they are always there, and the only methods of keeping them in check are candles, which are not placed by players. Contrast this to graveyards, which ARE fairly enjoyable: Phantoms do respawn, but you can take them out anywhere, any time for a brief respite. This puts the player in CONTROL of the situation. In future levels, I would advise against mechanics that cause the player to lose control. Grimalkins are also made worse by the sheer amount of damage they do. One thing that would make it more palatable is to allow shielding, giving players more control.
2. Harassment. Somewhat related to control, but players also don't like being harrassed. I actually do enjoy fighting the mini-monsters when they spawn en masse as a part of a scripted battle. However, put them on a respawner with no rewards, and now they are just harassment. This is also related to control, as there is no way to shut down the respawner. Part of the issue is, some of the mini-monsters use a continuous type attack like Wisps and Shankles, which makes them much more annoying to fight. Mini-jellies are less annoying, because they have long attack intervals, and slow, discrete attacks. Sometimes respawners are fun, but I'd like the designers to consider the boundary between challenge and harassment.
I also encourage others to think about first the superficial reason why they hate a level, and then dig deeper and consider what it is about that aspect that they actually hate (and share here).
That's why I specifically LIKE those stages. Players shouldn't be able to easily contain enemy encounters (part of the reason why I think Vanaduke is a fail boss).
People hate compounds because of the AE swarms of bunnies, not because of respawning bunnies. From what I've seen, the reception to Candlestick has been fairly positive among non-scrubby players.
I assume you haven't played Shadow Lairs yet, because they're FULL of situations where you aren't in control. Highly positive reception to Shadow Lairs in terms of gameplay.