Background: Our group does D&D 3.5/4e one week, and a different system the other week (we've done GURPS and Serenity, and I'm going to be running Mutants and Masterminds 3rd edition). I've (almost) always GMed the "other" week.
Something I've noticed is during D&D 4e combat, the defender doesn't have any impact in the battle. The attacker rolls "to-hit", then if he matches or exceeds AC, the attacker rolls damage and applies conditions. In GURPS and Serenity, the defender is involved in the battle -- either the defender has to roll a dodge / parry separately for the attack to hit, or it's a straight contested roll against a defense of the defender's choice.
This seems to have impacted the games:
- The flow for 4th edition seems to be faster. When it's player A's turn, everyone focuses on that person. In the other game, there's a lot of exchange between player and GM during combat (especially GURPS, with the "OK, I hit, now what type of defense do you want.").
- When the GM is acting in 4th edition, we know that we're not going to be involved. We're paying attention, but it's more like watching TV; we're not involved as much.
- In GURPS, a player rolls an attack really well, and then if I as a GM get a great dodge roll, that attack roll is nullified. Player is sad.
- Players can spend bennies on their defense roll -- this reduces the drama a bit on combat.
So, I was looking at the Mutants and Masterminds rules. Like D&D 4th edition and other d20 games (and unlike other games), M&M doesn't have a choice for the defender during combat. The basic attack system is "attacker rolls an attack, then the defender rolls toughness, with the target value being attacker's damage + 15." I was thinking that that can be simplified by "attacker rolls an attack, then rolls damage against the target's toughness rank (toughness + 5)." But, that essentially makes the defender not be involved at all in the attack process -- no dice rolls, nothing. I'm not sure I like that. But, does it matter in the long run?
TL-DR: How does the "flow" of combat change between a system like D&D 4e (where the attacker rolls all the dice to determine the outcome) and GURPS (where the defender has the chance to defend)? If I house-rule a game system from one to the the other, is there anything I need to worry about? Thanks.