(P) Combat Tactician; any successful melee attack is treated as a critical success.

Just checking that I understand this mechanic.  Someone who takes this permanently gets a critical success for any successful melee attack.  And critical success means a more positive outcome.

Can you elaborate how this plays out in a game? 

Hey Greymark, you've described it as written. If someone uses this as an action, then a success would give them advantage on damage and an advantage on the next round so the ability compares favourably to fast attack (attack twice) or mighty blow (double damage).

However, you may be aware that I am currently revising class abilities so these work similar to the proposed updates to monster abilities and this will likely revert back to a limited use ability to prevent it from being overpowered, therefore this may require a bit of tweaking for balance reasons.