As you must already know, there's two shows about the Borgia family currently running. One from Showtime, and this one here done by Canal +, an European TV channel. Ironically, both were filmed in the same country at the same time, but are completely independent productions.
People inevitably compare them both, and many often mistakenly claim the Canal + one is historically more accurate than the Showtime one, something that isn't true.
As a history aficionado focusing on the Renaissance era and the Borgias in particular, I can assure you that when it comes to historical accuracy the Canal + show is just as bad as the Showtime one.
Furthermore, the characterization isn't always credible in the Canal + version (and occasionally seems to change randomly and suddenly), while the Showtime version lacks in background details and in the people who should be surrounding the Borgias. So they each have their flaws.
Both of them have excellent points and are very entertaining as well though, even if every so often they both butcher the historical accuracy to quite amazing levels.
The Showtime version has a tendency to do shortcuts and to focus on character development (thus it succeeds in making you interested in the main characters), while the Canal + version tries to show more of the people surrounding them but fails to establish as good of a connection for the watchers, and also frequently veers off into bizarre tangents that are as bad or worse than the ones done by the Showtime version.
(A little list of some of the odd things in the Canal + version [SPOILER WARNING]: Cesare involved with witchcraft?? The whole sub-arc with Cesare trying to kill his baby?? The whole arc about Cesare getting raped and then having various post-traumatic reactions every time someone humiliates him by bringing that back up?? [end of spoilers.]
All of those are invented for the Canal + show and have no relation whatsoever with history, but the show also passes on rumors contemporary to the Borgias, that are known to be untrue and that the Showtime version did not pass on, thankfully. So claiming one is more historically accurate than the other is a moot point, imho. Both are flawed, and yet still very interesting and enjoyable.)
I personally prefer when historical series try to stay closer to actual history, but I realize that more often than not history is sacrificed for the sake of entertaining TV (it was so even with "Rome"), so I don't really blame either of the two shows for those inevitable peccadilloes.
In my opinion, both deserve a solid 4 stars. (I would give 5 for more historical accuracy, but the entertaining value of both is good enough to make it a 4 or even more despite the historical issues.)
Especially considering how we've gotten so much garbage fiction about the Borgias over the years; those two shows are surprisingly good compared so many of the past productions about them.
In conclusion, both are still extremely entertaining despite the issues with historical accuracy they both have. I strongly recommend watching them both if you're very interested in the period or in the Borgias.