It depends pretty much entirely on whether or not you like standard Shounen anime or not.
REBORN! kind of has a weird concept to it, but it's ultimately about the main character, Tsuna, getting more powerful and becoming Vongola X. The Vongola is a mafia family, and Tsuna is just an loser (the anime pretty much blatantly says that. lol) in middle school. He has no idea about the mafia, but a baby that can talk (I told you it's a bit weird) named REBORN! comes to his house as a "tutor" to tell him that he is the next leader of the Vongola family.
Beyond that, as I said earlier it's just like your standard Shounen. He runs into enemies that he and his group of friends have to fight.
Overall it's kind of hit or miss. It relies a lot on humor when it's outside of its main arcs, and sometimes that humor is just annoying. And one of the characters really annoys me. But that's just my opinion. The arcs themselves are pretty good, though, if you like Shounen.
It starts out incredibly slow, though. The first 20 episodes rely almost entirely on humor and are very episodic in nature. They're mainly just to introduce characters, but some of them can be a big of a drag. It's also hard to tell apart the filler from canon sometimes, and that's not good.
I actually only have a clear top six, but I'll try to make a top ten.
1. One Piece
2. Trigun
3. Fullmetal Alchemist
4. Ouran High School Host Club
5. Monster
6. Death Note
7.
La Corda D'Oro ~primo passo~
8. Nodame Cantabile
9. Samurai Champloo
10. Eyeshield 21
The list changes a lot... and I really didn't enjoy the bottom four anywhere near as much as I enjoyed the top six, and that's why it's hard to make the list. Although they are all great if you ask me.