I totally get why they didn't go with the BtAS style. A lot of people would have assumed that it was a continuation since they were already using the same actors for Batman and the Joker.

Before the movie came out I saw a lot of people complain that they didn't just use Bolland's art style. I see this complaint nearly every time they do one of these movies.

After the movie I think most people just focused on the part I don't like; the gross Batgirl retcon they added to pad out screen-time. I didn't like it when it was implied in the Batman Beyond show (or when they confirmed it in the spin-off comics) and I still don't like it here. I'm not sure what's worse; that she's his student, that she's his adopted son's ex, or that she's his friend's daughter. It takes a lot to make me hate Conroy's Batman but this relationship manages to do it.