First let me start by saying what follows is more of a guide to understanding the combat system, how to spec a character early on to be competitive on the PvP servers, and the utmost basic understanding of combative tactics in DC Universe Online.
For those more interested in the discussion of why "Oldschool" MMOers won't get it, skip to the end.
In DCUO you essentially have 3 major kinds of attacks that you can utilize with your SKILL set. Your skill set is essentially your weapons set, which is made up of combo skills and innate powers. Each set is comprised of these things, and each of them have counter attacks associated with them.
When you start a new character, the most important attacks to have are basic, and available to you within your first 3 skill points. To stay competitive in PvP you must get these first.
1) Leap Attack : You need your leap attack. This is usually a skill utilizing the holding of the left mouse button, or the Square button on the PS3 controller. (X on the 360.)
2) Block Breaker: You need your block breaker. This skill is usually done by holding the right mouse button, or Triangle on the PS3 Controller (Y on the 360.)
3) Combos: You need your first combo set. This may vary depending on the weapon skill you choose. Your first combo could knock down the opponent, knock up the opponent, or stun them.
4) Blocking/Rolling: The last ability you need to know is how to block attacks which is set as shift for PC, Right Button for PS3 and 360 (not right trigger)
Now for basic mechanics. I.E. Rock, Paper, Scissors. Please use the list above for reference.
A) When an opponent does a combo meant to knock down, knock up, knock back, or stun, you block. This will result in them being knocked down.
When an opponent notices a block and tries to utilize their block breaker, you leap attack. This will result in you stunning them.
C) When an opponent is blocking, you utilize a block breaker. This will result in you stunning the opposing player.
D) When you see an opening in your opponents defenses, whether they are knocked down, stunned, or knocked up, utilize your combos to keep them from launching a counter attack.
= stun / knock back / knock down / knock up
E) If you see your opponent block and roll, use a leap attack to stun them so that they cannot get away. This will result in you stunning the other player.
F) If you see an opponent utilizing a power that requires a charge time, you leap attack or combo to interrupt. Very useful against healers. This will result in stopping the player from casting.
> Powers with no instant cast time
G) If an opponent is trying to leap attack at you, blocking will knock them down instantly.
H) Lastly if and/or after you are knocked down, stunned, etc. use your block button to break out so you can continue fighting. For stuns it may call for repeated hitting of the left mouse button.
> stuns/ knockback / knockup
Following these basic steps will get your foot in the door for all those looking to PvP or for those just wanting to know more about the combat system and how it can help you in PvE too. PvE mobs will utilize knockbacks, stuns, etc. and knowing what these moves are and how to counter can be the difference between life and death.
Why do the "old school" MMO players not like this system? Theres no specific class structure dictating an advantage. A healer has no more advantage over a Tank who has no more advantage over a controller. There are no rock/paper/scissors classes, just attacks and counterattacks.
Theres no perfect mix of classes for your team members to win a battle, only the perfect mix of skillful players. Theres no click and wait for the next move, there are only actions and reactions, and quick thinking.
Theres no instant combination to win, nor are there pieces of gear that will overpower a player so much they will win every battle. There are gankers who gank the level 9 when they are level 20, and then the level 9 that kills the level 20 ganker. With the information above you may not be able to win every battle, but you'll make it damn hard for others to beat you.
Many games before this glorifies time spent and they have that time spent = your accomplishment both in the world and in battle. Here, a strong player can be known by his combative competency alone, and he can do so way before max level.
In this sense, the game is very progressive in terms of both combat, and level disparity. It may be quite possibly the most important part of the game, and one of the major pieces they've done right that will keep players playing. When the new blood coming in can be competitive as the veterans with just a little know how, it makes for a very engrossing game.