Hiking in Czech Republic, Poland and Slovakia: Conclusion

All three countries have a long hiking tradition and as a result the infrastructure for hikers is fantastic! Waymarking is excellent and often there are separate summer and winter trails which are signposted and blazed. Not to mention a lot of bike trails especially in Czech Republic. The trails are usually very well maintained mostly by use of hikers. Bushwhacking is really the exception, but logging activities can make trail finding difficult at times.
E3 uses existing trails here but is often mentioned on signposts (which is rarely the case in other countries!).
The terrain is usually easy or moderate - on the E3 I have not encountered any technically difficult trails. Sometimes ascents and descents can be quite steep and slippery in rain but nothing really serious.
In popular areas there are mountain huts which offer accommodation and restaurants. Expect big crowds in summer especially in touristy areas like the Giant Mountains or the Mala Fatra. You will encounter mostly day hikers. I have rarely seen any other long-distance hikers!

Resupply was easy and I rarely carried food for more than three days. Most bigger villages have a little store and in bigger cities there are all kinds of Western food store chains and discounters like Billa, Kaufland or Lidl. I enjoyed local specialties like smoked cheese and tasty string sausages which both keep a long time even in hotter weather. In supermarkets you can get the typical dehydrated pasta meals, cereals and snacks. Decathlon is widespread in Eastern Europe which means you can easily get new outdoor clothes or equipment if needed.

Water was not a problem - there are plenty of springs and wells along the trail which are usually marked on the free OSM maps. Just keep in mind that many springs are not piped but kept in a roofed "spring hut". You need some sort of container to scoop water out of there.
Tap water is safe to drink and therefore I never treated water in these three countries becausee I got it either from a tap or spring!
Wild camping is technically illegal in all three countries but I have never had a problem. There is so much forest that you can usually hide somewhere out of sight. Just plan ahead because the E3 traverses several national parks which are monitored by rangers - and for conservation reasons I would not want to camp there anyways.
I encountered very few hunters (which might have been due to the season) but plenty of lumberjacks and berry pickers. Commercial berry pickers work in gangs - so try not to camp in blueberry areas. These people are already up at sunrise so can have an unexpected early morning start! I was discovered once but nobody seemed to bother.

Hotels and restaurants are still a lot cheaper than in Western European countries although they are definitely up to Western standards. I usually paid around 30 - 40 EUR for a single room including breakfast and Wlan and never had any bad experience. On the contrary: Private hotels and pensions have by far exceeded my expectations. The same goes for restaurants: Quality was very high and I enjoyed local specialties like the ubiquitous Piroggi - dumplings filled with various stuffings.

The landscape I saw on the E3 was generally nice and interesting, sometimes even spectacular. But if you are looking for breathtaking views there are better places to go. Still what I liked a lot was the mixture of all those different mountain ranges mixed with different cultural and historical aspects. Parts of these three countries once belonged to Germany and/or Austria so you will find plenty of remnants. I read tombstones in cemeteries, explored churches and castles or came across leftovers of the two World Wars.

Don't be deterred by the language problem. Younger people all speak English and restaurant menus are usually bi- or trilingual. Beside English German is widespread.
To sum it up: I personally enjoyed hiking here a lot and I would definitely recommend it to a friend. If you are looking for relatively easy but interesting trail with a little luxury like staying in a hotel or eating in a restaurant once in a while, this is ideal - especially when you are interested in history.