Skyrim is certainly a much better value. The game itself is easily 4-5x bigger. Plus you can only reasonably replay DX3 once, unless your one of those 'must get all achievements' types. Where as Skyrim's replayability can be near infinite depending on how role-play inclined you are.
If you played MGS4, DX3 is a lot like that, only with a much less tedious story, and similar - but significantly worse- gameplay. The main characters' voice actors are even equally irritating.