It's a really fun game. I personally think it works best with a small group, where you essentially roleplay individual scenes for the characters at times that all interlock. So the knight talks to fellow knights about the conspiracy, Maesters talk to Maesters and that kind of thing. It gives things a much more intriguey feel.
As for mechanics. The social mechanics are really fun and novel when coming from a dnd background. Minmaxing is a problem, though as others have said, but really I never found it as much of a problem. Let players be badass at the things they're good at occasionally and then challenge them in the things they're poor at. Have the social player get kidnapped, or challenged to a duel without access to a champion. Have the knight get into fights that have political implications he can't handle. Families can essentially sacrifice their knights, and get the player tried for murder. Or a multitude of other things.
The war mechanics are quite good too. They're very crunchy, and as a DM I struggled, but if truth be told DnD crunch is a bit much for me as a dm sometimes so it might say more about me than the mechanics. Wars can take a while, so I'd use them sparingly as big game changers, rather than every session.
The house creation rules are great fun. It really gets creative juices flowing and soon even the less roleplay focused players are throwing out suggestions for why there was a demise in the house history, and that kind of thing. It's very fun and is wonderful starting place for plots as you think about the historical rivalries the house would have, and how they would try to get revenge.
As a warning, though, I will reiterate that it really does not suit larger game groups in my opinion. If others feel differently I hope they give advice, because for me it was a real struggle. I think the Goldilocks zone is anywhere from 2-4. Any more and, really, it's hard to have individual intrigue that makes ASOIAF special. Also combat isn't really fun for many character types, unless there's something to lose, meaning you can't throw a random encounter in like dnd to keep people entertained. Fighting isn't really a 'staple' of the game, more of a flavour for stakes and stuff, as the combat can be quick and deadly which is fun and has the right feel.
I think it's a system you have to really tailor to your players to make the most of. Putting in a lot of effort and giving players individual rivals is kind of a necessity to make the game interesting, but it is also some of the most rewarding DMing I've done.