Boxer engines have good points and bad points.
1) Two heads are better than one. Sometimes. You need two of everything and that costs more. The good news is that you can wrap the coolant jacket almost the whole way around the cylinder. The bad news is that you have to have more pulleys and gears than a Swiss watch to connect the left and right head. It is basically TWO 2 cylinder engines bolted together.
2) A taller deck means a wider engine. You've only got so many millimeters to work with between the frame rails. You can't just make a bulged hood like a normal car. That means shorter strokes and bigger bores. It also means space is very tight for stuff like Gasoline Direct Injection.
3) The engine is bolted together. That's good if you want to keep it together under high boost, but bad if you want to take it apart for some reason. You've got to remove the engine and pull the block halves apart for new pistons, rods, or a crank.
4) The crank is short and stout. The crank journals have a lot of overlap. The engine is naturally balanced because of the layout. All good, no bad.
5) The EJ-series Subaru engine benefits from the big bores because there is very little valve shrouding. The heads have plenty of room for ports, but Subaru still found some way of putting a dogleg in half of the exhaust ports (!). I expect that to be one of the things that isn't in the new head design.
6) Boxer rumble: The engine fires off 4 cylinders just like any other 4 cylinder engine. The rumble comes from the cast iron exhaust manifold. I've seen some pictures of SS long tube equal length 4-into-1 headers that not only change the sound, but the whole character of the engine. The collector is back by the transmission and the four primary pipes dump straight into it.
7) How low can you go? The boxer engine only has a few things underneath it; the oil pan and the exhaust. Let's hope Toyota found a way to drop the engine down a bit. I'm thinking; an oil pan with wings and exhaust ports pointing 60 degrees towards the rear of the car.