Personally, I like Splice, but like with a lot of horror, it's a film that is entirely dependent on the attitude you go into with. If you're ready to pick it a part and discover its insanity, it's there, but when you're on board for a pretty serious film with a fair amount of heavy subject matter, you can get a lot out of it. It raises some questions on relationships and the moral dilemmas associated with modern science, but never goes far enough with them to make it a great film.
In the end, it's captivating, but there isn't much that pushes it from being more than slightly above-average. Pretty middle-of-the-road for a HDTGM episode, imo.