The rule system
The rules are presented in a clear and concise way and I think they are well adapted to the setting. For those anxious about leaving Call of Cthulhu, I can comfort you with the fact that the new DG rules stay in BRP-land as they are built from the Legend SRD (from Mongoose Publishing). This means that DG now has more in common with all the games derived from the first Mongoose RuneQuest SRD - Mongoose RuneQuest, Legend, RuneQuest 6/Mythras, OpenQuest 2, Renaissance etc. In fact, this game is closer to 6th edition CoC than the new 7th edition CoC rules. Over all, the game is vastly simplified (shorter skill lists, more generic weapon lists and so on) in comparison with the old DG books which had tons of new stuff for CoC. And this is a good thing in my book.
At the same time, some new mechanics get introduced:
Critical successes are now 01 and doubles (11, 22, 33 etc) under your skill. So if you have a skill of 40% you will crit as in the example above. At the same, fumbles funcion the same - 00 and doubles over your skill are fumbles (in the example 44, 55, 66, 77, 88 and 00 would be fumbles. I like this system as it allows crits and fumbles to scale after actual skill level.
Another new thing is the Luck roll that now is a flat 50% chance that things will go your way. Or not.
Opposed tests are resolved by both parties rolling and the highest success wins, which has been standard in the RuneQuest SRD line of games for many years.
Willpower points are also new. They can be thought of as mental fuel or mental hit points. You don't want to run out of them. They are based on POW.
Combat is a bit different than both old DG and new CoC 7th ed. A combat turn is a few seconds long and a PC can make ONE action in that amount of time. If you choose to Parry or Dodge, your action is gone for the combat turn. There are a bunch of combat actions described, both offensive and defensive, allowing for a resonable amount of combat tactics. Another cool new thing is the Lethality Rating for more dangerous weapons. This is basically a % roll to determine if a target survives a hit by the big bad gun. If successful, the target (if human at least) immediately drops to 0 hp. This is to avoid the old rules where you had to roll separately to determine number of hits from autofire which could mean a lot of rolls. If you're not a fan of the Lethality rule, there are also optional rules more in the vein of the old autofire rules.
Good old Sanity has also gotten an overhaul. Basically, there are three conditions that might cause SAN loss - Violence, Helplessness and the Unnatural. This is cool, as now your sanity isn't threatened only by monsters and their kynde, but also by malign actions of other people or feelings of not being able to do something. Very much in the line of what DG is about. Otherwise thresholds are pretty the same: 5 or more SAN in a roll is temporary insanity and 0 SAN is permanent insanity. Sanity Points are POW x 5 as before. The concept of Breaking Point is however new. This is described as SAN minus POW and if your PCs loses SAN below the Breaking Point, they get a Disorder and must reset the Breaking Point to current SAN minus POW. The effects a PC suffer when being temporary insane or having a disorder are very good and designed to both realistic and playable. Another cool thing is that a PC can adapt to violence and helplessness (but never to the unnatural), meaning that being in those situations won't call for a SAN roll any more. However, the PC also loses Charisma and from his or her Bonds. Bonds are also a new concept - it can be the relation with a spouse or kids, or with other agents or groups. Bonds are what connects the PC to humanity. So, losing your Bonds will make you more inhumane and also more susceptible to psychological trauma. This feels realistic and might form a very good basis for role-playing. I must confess that I haven't grasped the concept of Bonds 100% yet, but I guess it will be clearer in actual play.
When it comes to PC wealth, expenses and bying of gear, DG introduces a fairly abstract system where you don't have to track every dollar for your PC. Some stuff are day to day cheap and the game just assume that the PC can afford it. Other things are more expensive or restricted and it's up to the GM to decide if the item is obtainable. I like it, but this is one of the things that must be tested in-game.
Contrary to "standard" Call of Cthulhu, where most investigators are average Joe's and Jane's, DG assumes that the PCs are members of a monster-fighting organization and that most PCs (or Agents as they are called in DG) are employed by some Federal Agency. Consequently, most occupations in the book are just that. Examples are FBI, DEA, the military, CIA and so on. There are also a bunch of more civilian occupations in the book as well as advice on how to creat your own occupations. The old DG books had the US agencies in the core book and then lots of international agencies in the other books, supporting Agents from nearly all countries. The new DG book is focussed solely on US agencies, which I feel is resaonable but I still miss GRU-SV8 (Russian) or PISCES (British). Hopefully, they will be in the forthcoming books from Arc Dream. And I'm so planning to do the Swedish agencies, DG style :)
The new version of Delta Green promises to be an awesome game. The books released so far are pretty and sturdy, with well-written and appropriate rules for the setting/game concept. If you like old Delta Green I'm sure you'll gonna love new Delta Green. However, for players and GMs new to DG, the Agent's handbook is a bit thin on the DG "mythos". Hopefully, this will be remedied in future publications. And don't forget - the old DG books are now available in PDF form from DriveThruRPG, so they can be mined for ideas, adventures and background.
[5 of 5 Stars!]