Stock for stock i think the N55 feels better than my N54 E90. Sounds and feels a bit smoother. Having a tune on it thats a different story because the N54 makes a ton more hp/tq. I hit 350whp and 400wtq with just a tune and exhaust with my N54 where as now i am probably barely getting 300whp and 350wtq with the same mods.
Seems like a lot of the enhancements listed above makes the motor less robust compared to the old motor though. lightweight sounds like less strong to me. I believe the N54 had a forged crank,rods and possibly pistons which is why guys have already pushed that motor over 500whp without any issues.