For me, the biggest disappointment with Realm of Magic was that they chose not to do anything with toddlers and children in this pack. I would have loved it if toddlers had manifested magic accidentally or spontaneously by doing such things as teleporting themselves at will or fetching a toy or a snack, and also if kids could have done a few simple spells, perhaps child versions of the adult spells like in TS1, or even just summoning little pixies or sprites to play with them. (If they were going to give Sprites to secret society members in DU, there's no reason why something similar couldn't have been done for the smaller sims). Even a small amount of gameplay for the younger sims, along the lines of what we're getting with Nifty Knitting, would have made this pack feel more complete.
As for the magic realm, there are a lot of things I love about it. I love the shops area and the rotating wares on offer (great for collecting); I wish only that they would have added an eatery of some sort with a unique recipe (pumpkin juice? magic mushroom risotto?) or two so that sims could congregate and eat in front of a food stall (like the sort of street vendor that used to sell roast chestnuts etc in Victorian days). I love the main house, with random sims duelling and casting spells, and I don't mind the bare bones quality of it because the lot is editable. For instance, I easily made it into a training academy/ dormitory with a really creepy library full of dead things and I like it much better than I would have liked an uneditable lot. I do wish they had given us a quest or two for the other parts of the world, like making the new plants harder to find or otherwise giving us something to unlock, such as by going to the greenhouse and finding a magic way inside. I think some goal-oriented gameplay (besides simple gathering of spawned plants) would have improved that part of the world. In general, I wish there was an extra incentive to becoming a maxed out, powerful spellcaster, such as ascending to join the sages and helping in some arcane ritual to bind the world together more (complete with some unique and special animations of brief reintegrations before everything is constantly breaking apart again). But the appearance of the world (including the greenhouse and duelling grounds) is wonderful and really adds a lot to my enjoyment of the pack.
I like the spells and I don't find them as grindy as TS3 spells were. (I got so sick of conjuring that silly apple). For me they don't approach the beauty and completeness of the TS2 spells, though. The only thing they do better than TS2 is that they do not limit any of the spells or potions to a certain type of witch (good, evil, neutral) which was a definite downside there. Having to craft reagents in the cauldron to act as ingredients was also really grindy and could be annoying at times (although the secret lots helped a bit in that sims could level up their skill more quickly there). Luckily, LittleMsSam's mods have greatly improved the original spells and there are some creative ones available for download to add to the ones we were given with the pack. I would love it if, alongside some crosspack functionality with future packs, they updated the spellbook to add a new spell from time to time (although I don't really expect that to happen despite the fact that it would be really nice).