Ryuki's ending is what is known as a "Deus ex machina". Only difference is that life continued without Yui or Kanzaki. Not exactly the way I would have preferred the series to end, but given the multitudes of Riders and the multiple sections of the story, it did wrap up everything somewhat nicely.
What I notice these days is that newgen kamen rider series tend to leave things a little open. In 555, while the dismantlement of Smart Brain does help to prevent orphenochs from going crazy or fighting humans, it doesn't solve the fact some people will eventually become orphenochs too, or Takumi's lifespan issue. In Blade, while Kenzaki's self-sacrifice did help to prolonge the time Hajime can spend as a human, the threat of two Jokers still existing is very real, leaving the actual threat unresolved as opposed to the movie's ending. (at least based off what I read, haven't seen the movie). Kabuto did a somewhat better job at tying loose ends in regards to most of the Riders, but a lot of questions went unanswered regarding past events or Kamen Rider Kick Hopper. Odds are by the end of Den-O, a lot of paradoxical questions will be left unanswered.
While it's not necessarily a bad thing to leave some things open-ended as opposed to just saying "it's over", it can be annoying at times.