Mirai Nikki features a fair amount of cliches, sure. A disenfranchised school boy protagonist, a life or death game with high stakes, predicting the future, etc. But it also has a lot of original ideas and elements that make it fresh and new.
As I mentioned before, the plot revolves around a fella named Yuki and his finding of a cell phone diary called a "Future Diary" which allows him to see into the future. He must use this diary to win a life or death game of which the winner becomes god himself. There features lots of wonderful characters, namely Yuki himself, and his stalker/girlfriend, Yuno.
The story begins normally, with a normal blank slate bored school kid finding a great power etc etc. The thing that is interesting about this series, though, is that he doesn't remain a "blank slate" through the whole series. He matures and grows and undergoes a healthy, good character development.
The plot holes at times can be somewhat gratuitous, particularly near the climax, but they can be overlooked for an enjoyable experience. Near the end particularly, the plot becomes such a clusterfuck it can be hard to tell exactly what is happening and where the stakes are.
The animation isn't spectacular, but it isn't bad, certainly. I probably would have given the animation a lower score if not for the pristine OP this Anime has. The OP unfortunately gets a makeover halfway through, which is unfortunate, but I really love the original OP.
The OP also has very good music, it begins as a haunting choir and gives way to radical guitar shreddage and great OP footage. The music for the actual shows aren't terrible, but they aren't anything special, either. If not for the OP, they would be run of the mill.
When considering watching the sub vs dub, it's really up to preference. There's not much major difference in quality, the subs and the dub work well for what they were trying to convey, and neither really fits the action better or worse. It's up to which you like more.
The characters of this series are the best aspect, certainly. Every Diary User is an interesting, original character who you get to know and love. Every Diary User is given at least some back story, some reason for them to want to become God, and they all manage to be very believeable. I think I could easily remember all of them, because they are very memorable, they all leave an impression on you, and you're a little sad to see some of them go.
The best character, in my opinion, is Yuki's stalker/girlfriend, Yuno. If nothing else, watch the show for Yuno. She's crazy, she's fun, she's sad, she's a character. She's crazy, literally.
If you have some time, watch this anime. It's worth whatever time you give it. It's not one of the best animes ever, and it's not particularly extraordinary, but it is a wonderful experience.