I've played a decent amount of Shadowrun 3rd edition, and recently joined a group of players who play 4th ed. I know I'm going to get confused and turned about- In summary, what's changed that I should reread about, and what's similar enough (but different in an important way) that I would otherwise assume is the same and would get tripped up about?
[RPG] What are the differences between Shadowrun 3rd and 4th edition that I should know about
shadowrunshadowrun-sr4
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The major changes I noticed between the two editions are as follows:
Limits prevent characters from being overly min-maxed. Each of them is centered around an attribute that is typically dumped in normal characters; the most important attribute for the physical limit, for instance, is Strength, though other attributes weigh in they have the same impact as Strength does alone. This means that you can't build a "never gonna fight close quarters" build and just dump strength and expect to do well in other physical areas, encouraging a well-rounded thing.
Mystic adepts get a huge buff. I'm not exactly sure that this is a bad thing; they still can't astrally project, but they get the powers of both mages (other than astral) and phys-ads pretty nicely. Were they still using the BP system, this would be a flaw, and I'm not sure about allowing them as the third pick on your priority system, but I think the reason that people are upset is because they don't astrally project as much as they should when not a mystic adept.
The priority system really makes things a lot better. It prevents some of the worst cheesing during character creation (don't get me wrong-it's still possible, but you have to know what you're doing and make some sacrifices).
Combat's been changed rather heavily on the bookkeeping, but not so much the execution. The Accuracy limit keeps pistols from killing Great Dragons, which is a nice touch, but also discourages just dumping into the newly increased skills and maxing them out right away. It also makes smartlinks a more tangible advantage, as do laser sights. Armor is now a single rating for stun and physical, which makes it a lot easier for new players to understand, and, in my opinion, more realistic.
Hacking's a lot better. Mind you; the wireless thing contains some logic holes and gimmicks with the new benefits it gives stuff like cyberware or laser sights, but hackers can enjoy a target rich playground with new rules for hacking that make prepping a hacker 90% easier and playing one about 50% easier; GM'ing hacking also became a lot easier. In addition, some of the more broken technomancer stuff has been revised so you now have a reason to play a decker instead of a technomancer every single time.
All in all, it's faster and more streamlined. If you want my "reviewer" version, you can check it out on my blog, but I've said pretty much everything I said there here, only without the sales pitches.
Basic rolls
You roll as many d6s as your Attribute + Skill for the intended action. Each dice rolling a 5 or 6 is a "hit". If there is a difficulty, the "net hits" are the amount on hits above that difficulty.
A player has to roll Charisma + Etiquette, with a difficulty of 3. His character has 5 in Charisma and 3 in Etiquette. He rolls 8 d6s, and 4 of them roll a 5 or 6. That's 4 hits, or 1 net hit.
"Basic" combat mechanic
1 - The attacker rolls the appropriate attack skill + attribute + modifiers.
A street samurai fires a single shot at a non-moving target. He rolls Agility + Pistols, for 4 hits.
2 - The defender then rolls the appropriate defense skill + attribute + modifiers.
This depends a LOT on how the target defends. For our example, let's say the target just rolls his reaction to jump on the side, for 1 hit.
3 - You then compare their results. If the defender rolls more hits than the attacker, or on a tie, the attack misses. If the attacker rolls more hits, the attack succeeds and the net hits is added to the weapon's Damage Value.
If the target had rolled 4 hits or more, nothing would have happened. The attacker rolled more though, so the 3 net hits are added to the weapon's Damage Value. The weapon had a Damage Value of 6P, it becomes 9P for this attack.
4 - If the attack succeeds, the defenser then rolls Body + Armor - Weapon Penetration. Each hit reduces Damage Value + net hits of the attack by 1.
The target has a Body + Armor of 7. The gun has a Penetration of -1. The target therefore rolls 6 dice, with each hit reducing the modified Damage Value by 1. He gets 2 hits, reducing the modified Damage Value to 7P.
5 - Finally, you apply the final Damage Value to the defenser as wounds (i.e. nothing if it is reduced to 0).
The defenser takes 7 wounds, and crosses 7 boxes of damage on his sheet.
This is the combat mechanic reduced to its "simplest". However, keep in mind that a LOT of modifiers and exception then apply, depending on whether the attacker or defender is moving (or both!), whether anyone is behind cover, the weapons rate of fire, who is already wounded, recoil, and so on.
Drones and Magic
Drones and Magic are both two extremely complex and detailed systems of the game, therefore it is almost impossible to sum them up in a couple of sentences. I will give some guidelines, but take them with a truckload of salt.
Drones have their own mechanic, but basically and in a lot of cases, there will be a hacker using his Mental attributes + hacking skills to attack/defend instead of standard attribute/skills.
As for Magic, there are even more things to take into account. In a lot of situations, spells will be cast using a Mental Attribute and the Spellcasting skill, and will be resisted either through Willpower or normal defending attributes. They also cause damage to the casters. Remember though that there are a LOT of different spells, of ways to cast them, as well as Adepts and Spirits.
Best Answer
Shadowrun 4 uses a largely different mechanic from Shadowrun 3: SR4 uses the new World of Darkness dice mechanic rather than the classic Shadowrun mechanic (except they use d6 instead of d10, but 66.7% and 70% are basically the same probability...). The justification for the change was to speed up combat and other conflict resolution, which it does to some extent, by not having to keep track of both target number and number of successes (all target numbers are now 5; some things have thresholds for the number of successes you need--all the math is just done on # of successes). Also, dice pools are gone, so there are many fewer tactical decisions to make, also speeding up the process. (If you enjoyed selecting just how many combat pool you were going to use for soaking so you had enough left to take out your next opponent with one shot, you will be disappointed. If you were annoyed that you had all these extra decisions to make when you really just wanted to kill the bad guy as quickly and effectively as possible, you will be pleased.)
Because of the drastic change to mechanics, SR4 is a dramatically less versatile system; it works with a much narrower range of abilities and difficulties. On the other hand, the game has been balanced so that a normal run will be right in the middle of the sweet spot where the outcomes in SR4 do not feel drastically different from SR3. So if you were doing standard runs before, and will be again, you can take advantage of the simpler mechanics without much loss. SR4 breaks badly as characters or NPCs become extremely powerful (e.g. you need an impossible number of successes to defeat them, with d20-style "I stand in the middle of a room full of goblins for hours and they can't hit me" scenarios), so there are various caps and limits that were much softer before; starting out, you can make a runner who comes pretty close to the best in the world in something. Whether you like that or not is personal taste, but it is definitely a difference.
Anyway, the take-home message is that you should be prepared to feel like you're playing with different mechanics. The same concepts are mostly there in some guise, but it scarcely would have been more different if they had switched to d20.
Despite the mechanics changes, the setting feels much the same as before. Otaku are now Technomancers, and the old separate-worlds idea of the matrix has been replaced by a parallel augmented reality version that greatly helps with integrating deckers (now hackers--no more decks!) into the flow of gameplay. The timeline has advanced another decade or so, but aside from the crash of the old Matrix and replacement with the new augmented reality stuff, there's nothing that will radically change how your character approaches the world. The new mechanics are balanced to yield similar outcomes for standard runs, so you'll be approximately equally worried about a team of security guards or whatnot; if you were using SR3 the way you were "supposed" to be, you'll mostly just notice that SR4 runs a bit faster and that you can see your decker face-to-face.