My chief complaint is that they used the same ham-fisted editor (or at least the same editing style) as Half-Blood Prince. Many arcane details are left in with no explanation at all. The time (only a few seconds each, in many cases) that should have been spent explaining was instead devoted to needless special effects. If you've read the books, you'll find DH1 to be a good visualization of the action. If you haven't, or if it's been a while, you'll be completely lost within minutes and have to spend the next two and a half hours being thoroughly confused.
Sure, the Blob was never a thin mercenary. Sure, Wade Wilson wasn't a mutant. But what a storyline! And we learn Logan's real first name. Definitely a good action movie.