I haven't played Arkham Knight but I can kind of see Sifr's point, especially given the story background.
However, I am not sure how comparable this is to ME. If we are really exploring new worlds and lot's of terrain, than frequent use of the MAKO would make more sense in ME:A than the Batmobile might have made in BAK. And also, protagonists in ME are not required to have as many scruples as Batman, especially given that we don't even know our potential adversary. At least as far as the story is concerned.
As for how much fun it is, well, that will depend on it's implementation I guess. I do seriously hope that vehicular combat will be part of the MAKO gameplay. Just rolling round would just get old pretty quick.
The major complaints about the batmobile that I've seen are about how frequently it's thrust upon you in required mini-game like sections.
Need to save someone? Here's another annoying Riddler RaceTM.
Need to beat a boss? Here's the same tank battle, but with more people.
Problems arise because there are prescribed parts of the game that can only be accomplished with the Batmobile. The quick free-flow combat is replaced with essentially a different kind of game with no wiggle room. Compare that to Halo's "vehicle sections," which are essentially normal combat scenarios with larger arenas and tougher enemies. Obviously, you're meant to drive in this kind of section, but you're allowed (and often forced) to swap back and forth between mounted and foot combat. It's more fluid.
As long as BioWare present the Mako as a natural extension of the exploration (and make sure that it controls properly), then they won't fall into the same hole as Rocksteady, and considering that BioWare are taking car advice from Need for Speed, I think we'll be fine in the controls department.