Very favourably I would say. The cramped and fairly linear levels have gone completely, and now you have huge sprawling playgrounds in which to conduct your bollock-popping activity.
The levels themselves are very varied too. You start in a beautiful seaside town similar to Hitman's Sapienza for example. Graphically it is very pretty and also very stable - I haven't come across a single bug as yet which for a day 1 buy is a rarity indeed. SE3 was a buggy mess, and my recent playthrough was always curtailed when the game crashed.
Rebellion also seem to have realised that while the sniping is fun, actually the ability to use the sniping to set up awesome chain reactions is more fun. As an example, you can now set up booby traps on the bodies of the slain, bodies which always attract attention. Maybe you take advantage of the Luftwaffe flying overhead to score a 'silent' kill on an outlying sentry, booby-trap his body, back away then throw a rock to attract his colleagues to investigate, spot the body and trigger the explosion. Maybe you have seen a patrol approaching - you can set your S-mines to explode on the first or second footfall to hit them, to ensure that they don't go off until the patrol is far more centred on their position. Shoot out a winch to squish unsuspecting nazis below. Pepper the approach to your location with mines and then blow an alarm whistle to bring the baddies running in. Shoot nearby barrels, truck engines, weapon stickpiles, fuel cans etc and blow folks nearby to kingdom come.
The bullet cam is greatly improved in that shots are animated much more quickly for the most part, while still lingering on the grisly bits. Also 'improved' is the gore-fetishisation of the bodies themselves, much attention has been paid to the blasting out of teeth, wibbling of splattered brains, and of course sniper-aided castration.
It is not all good - you still play Lieutenant Gravel-Voice, with as much personality as a rock. The script is rizla thin, the voice-acting terrible, both in its delivery and also it serving purely as a plot-exposition dump. That said, I don't care much about any of that. At the start of each mission you get to speak to each of the cast members, and they will give you an objective. Hit space to skip the acting, just get your map updated. Then use the radio to get your main mission, then off you go. Having some context is fine, but once you are into the mission proper it is you, your rifle and various nefarious traps, the landscape and lots of nazis.
My only gripe is that if you complete your main objective, on occasion that is it, mission over. I found this to my cost - I had a mission to destroy a huge rail-mounted artillery piece that was firing from atop an aqueduct, with secondary objectives to find a downed spy-plane pilot, destroy the remains of the plane, and also blow up an ammo dump. In the previous mission I had had to exfiltrate on completing my objective. I worked around the map, found two armed checkpoints that I cleared for some extra XP, destroyed the secondary then primary ammo dumps, and found myself overlooking the aqueduct. Taking advantage of the old 'sabotaged generator' to make noise and cover my assault, I sniped and sniped until the aqueduct and far bank were clear of nazis, planted a satchel charge, and moved to the far bank. The downed plane and the pilot were both a little way off, but I wanted to see the boom so worked my way round until I could get a bead on the satchel charge and blew the whole aqueduct, including the gun, to kingdom come. Mission over. After nearly 2 hours in I had the option of continuing taken away. WTF?
Ah well, will replay that one - it was loads of fun anyhow so no great loss.