Seat selection might be possible but painful considering the UX on their website, which can look totally different depending on which version you browse (fr, us, hk...). Though you may be more successful if you try to contact them by phone.
From what I have experienced on a recent trip though, seatmap remains still fairly open during OLCI and it's not that hard to catch a decent seat.
Regarding their IFE, they are pretty new with a correct selection of films (but maybe more "east-oriented" than on AF as you could imagine). AF IFE can't be beaten on the music selection.
Overall I would not hesitate to take MU again if the prices are in the same range as AF. I've read a lot of reviews before taking my flights regarding weird things (e.g. crew smoking in the plane...) but nothing of that happened.
Finally, you might also considere miles accrual for your choice. I've just returned from a trip on MU earning 50% on FB although the tickets were very cheap.