WITCHER 3 is much much better than DAI
Story is better - Personal compact story unlike world saving BS we see in Bioware games...
Characters are better..- Damn i love Ciri - What a classy well developed female character..
Graphics (though downgraded compared to original target render reveal) - Better tha DAI...Game is huge with dynamic weather and all..Game runs great on Ultra on PC.. 
Better side quests - Excellent rewarding side quests with deep back story compared to shitty fetch quests in DAI....
Better Dialogue system with no obvious blue or red options..
Choices matters and they affect main story...Ending changes based on your decisions in side quests...Game also gives you multiple playable epilogues..
No microtransaction BS...Free DLC every week...Total 16 free DLC will be released...
World feels and look more realistic than fake static world of DAI
NO DRM ON PC (GOG)
Overall a much better experience than DAI.
Plus game will have full mod support as well... 