Although this sounds fairly straightforward, it can cause issues! For example, you may want to give your spouse everything on first death, but if on second death the value of the whole estate is over £2m, then you may not be able to benefit from this new allowance at all, depending on how far over £2m you are (£2,250,000 for example, means you have no allowance left - so the most you can leave tax free to anyone other than your spouse will be £325,000).
We have spent many hours at Oliver's Wills, attending seminars and listening to industry commentators about this new allowance, and while it is a good thing if you have an estate over £325,000, and have residential property, and have children etc., everyone should get advice about how to plan for this allowance and whether your Will should be amended or left as it is.