Combat XP got a straight nerf. Previously 50% for all tanks, now limited to non-premium MT/HTs only.
Crew XP/Free XP increased for specific tanks, but again I'd rather have the 50% bonus across all tanks.
Credit bonus is also technically nerfed, now you need to complete ALL 5 decoration books to get 50% bonus, where previously you only needed to complete 1 specific credit book. ie You'll get 10% bonus if you complete only 1 book, which I'm assuming will increase the shard cost by 4-5 times to get the complete 50% credit bonus.
Overall I like the other new features/rewards, but the tank slot feature should've been in addition to the typical previous year's combat/crew/free xp bonuses imo, NOT replace them.