Too short, too easy, but not bad in *every* aspect.
The search for Triwizard Shields and Cards made for some fun activity, but the lack of explanation as to what they're actually for (at least, in my eyes - I bought the version with the Dutch manual, perhaps the original elaborates further) made it feel a bit pointless. The biggest anti-climax for me came with the 'final' battle, the Dark Lord Voldemort, which was by far the easiest Big Boss I've ever played. His attacks were easy to avoid and even a grand magnificent row of subsequent (deadly?) yellow blurbs failed to pose a proper risk.
Now, onto the better aspects. The graphics were fine, and the 3D-battles were done brilliantly in my opinion, although - once again - I was thrown a bit into the deep at first with the three available combat modes. My two helpers, computer-controlled, cooperated with me fully when I asked them to and even when I hadn't. The variety of spells given could be used in a similar variety of manners, ranging from unlocking chests to extinguishing fire crabs for once and for all. The levels all had their own distinct feel, enhanced some more by the nice movie-like cutscenes at their beginning; I especially liked the way the Prefect's Bathroom and the grounds around Hagrid's hut were portrayed.
The mini-games unlocked throughout the game were fun aswell, although not as much as those in SM64DS, mainly because there's less of them so they tend to get repetitive earlier. I thought the Yule-ball was especially amusing, with Ron, Harry and Hermione each having their distinct way of moving about.
All in all, I personally would not recommend buying this game unless you're an absolute Harry Potter-die hard and don't mind the lack of story or some nice interludes giving you a feel of Hogwarts like in The Philosopher's Stone for the Gameboy Color way back.