I remember first version sc3 and tutorial how to play and used special abilities of units that was masterpieces. Also story mode is with infectors with infected terrans, templar kill energy units, thor have energy … - all is working!
Next sc2.part2 little destroy this fable but it is still acceptable long range units not impact too much fable. Game need some skills.
Next sc2.part3 impact story and gameplay become clash of armies - no control units and they have not impact - you force to play boring fast games - no strategy at all - who do more units is better 
Current version (impotent infector without infector is really against story - why infector can not attack - to make game even shorter and more boring?) . I play sc2 many times and like it but now it bloody brawl like shooters - it is not strategy any more - now only important who do units faster.
Terrans do only marines and hurra, zergs same, protos same … - combination of units is completely not important - there is not any balance.
If you not understand what does mean try play Sc2.part1 where all was tought and all units have different use and there is multiple combination attack/defence.
No there is no defence only attack - from real time chess it become simple shooter
Explanation of my names:
Sc2.part1 == Wings of Liberty (the best version ever - true rts chess! - the best tutorials for units and their skills - the most balanced)
Sc2.part2 == Heart of the Swarm (nice also but little worse balance)
Sc2.part3 == Legacy of the Void I (worse than previous)
Sc2.part4 == Legacy of the Void II (infector impotent without infected terrans that most boring multiplayer - on shoot no defence/attack)
That is my feeling from playing multiplayer through years.