Here in the Netherlands we have currently 80% coverage in the whole country, which will be 100% in 1 or 2 months.
I noticed my signal strength and quality on 4g is more than 200% better compared to 3g, especially indoors.
With 3g I used to get 0-2 bars of signal strength on a certain place indoors. Now with 4g it's maximum signal strength on the same location.
This also applies to data transfer rates. On 3g it seems sloooooow to load stuff, but with 4g it's the same speed as on WiFi, pages load instantly and without waiting times at all.
4g also seems much easier on the battery. It barely drains battery on 4g, even with (very) low 4g signal strength.