So I've recently been playing in a game with a Lightfoot Halfing Rogue. This is a list of my findings with the Race/Class and game mechanics as a whole.
Advantage/Disadvantage: As noted by many, the Advantage/Disadvantage mechanic is very good, however the fact that any form of disadvantage cancels all forms of advantage and vice versa is rather irritating. On more than one occasion I have had multiple forms of advantage, and one form of disadvantage ruins my entire roll.
Saving Throws: I have had few occasions to make a saving throw, but currently the setup seems to work.
Hit Dice and hit points: I noticed that rolling for hit points still has that horrible chance of getting a 1, which is not only frustrating but can ruin a character with several bad rolls. I suggest an Advatage style mechanic. When rolling for HP at level up, roll twice and take the best result. This way, someone with a D6 only has a 1/36 chance of a 1, while a D12 has a 1/144, thus making higher Hit Dice very relevant.
Skills: The skills being assigned to a single ability score again feels badly implemented. If I make an attempt to Intimidate someone, why should I be forced to use Charisma when my Strength is higher and more appropriate?
The skills should also be more condensed. Why are Listen/Search/Spot not just Perception. I know it makes that a very strong skill, but it simplifies things. The same goes for Balance/Tumble and Climb/Jump/Swim. Making them one skill is something 4e got right. Other problems are redundant skills like Break an Object. Next Intuit Direction will be back. Do away with things that can be covered by other mechanics like attack/damage rolls.
The skill die is currently to spaced out. It should start at a D4 and have 4 increases at lvls 5,9,13 and 17 to still end at a D12. It may be a smaller bonus to start, but offers more option for people who want lots of skills and makes little difference to people who want a high skill dice.
Feats: I really like that some class features (like the rogues) are now feats. It removes the need for a Skill Monkey character, thus leaving party class choice broader for the average group. The addition of Bull Rush/Charge/Disarm feel forced though. These are mechanics that anyone should be able to do and having the feat just would make you better at them, similar to Dual Weapon Fighting.
The specialities seem a waste of text at the moment, but could be easily fixed with my next suggestion.
There are to few feats over the life of character. Ignoring the fact that feats stop after level 9, having only 4 feats over 10 levels isn't enough. However, offer to many feats and someone can become exceptionally good. The way to solve this is to have the specialities offer a set list of feats at levels 1,3,6 and 9 that cannot be altered. Then players can choose any feat they want at levels 2,5 and 7. This nearly doubles the number of feats, but over half of them are pre determined by the Speciality.
The change that now gives races two Ability Score increases is very welcome. It brings the other races more in line with humans, as your ability scores are the core to defining what a character can do.
The change to Lucky was a bit disappointing, but I also disliked its previous incarnation. I would prefer a simple reroll, that recharges after a short rest. Similar to a 4e encounter power, it would give the chance to fix a very bad roll, but luck is only on your side so much.
The loss of Halfing weapon bonuses is something I really miss. I like the thematic feel of using a short sword and sling because it fits the race better. But now there is no mechanical reason to use them instead of a Rapier and Short Bow. Racial weapon bonuses should help make weak weapons viable for certain races without being stronger than other options available.
The additional languages is also welcome. Having a high Intelligence character have multiple languages makes sense, the only problem is I could see a list of available languages. i may have just missed it.
Everything else about the Halfling I like.
I know the Rogue is currently in transition, but It has many flaws that need addressing.
First is the loss of Skill Mastery. The ability to roll your Skill Die twice wasn't much of a bonus, but did give a Rogue an edge as far as an Expert style of character goes. If a fighter and a Rogue both have the Disarm Traps feat, the rogue is still slightly better because he can roll twice on the skill die. This is a small bonus, but its loss really hurts my view of the rogue as a skillful class.
I'm glad to see skill tricks gone. Most only weakened your skill attempts by wasting your skill die on strange gimmicks. Having some appear as feats is something that makes perfect sense and works well.
Sneak Attack, now this has been debated a lot, and I have to agree that I currently don't like it. At levels 1 and 2 it actually lowers your damage per round, and only starts getting useful at 2D6+. Then at higher levels it gets far to strong. Adding +10D8 to damage is a heck of a lot of damage. I would personally change it to only work on Advantage, but doesn't provide disadvantage. It would start at 1D6 and increase 1D6 every four levels (5,9,13,17) and then increase to D8's as a class capstone. So at lvl 20 you do 5D8 extra damage.
Backstab/Isolated Strike are excellent mechanics, offering a chance for advantage on around 50% of attacks. I highly support this class feature.
Bonus feats from rogue schemes seem to be to few. They are replacing class features that were lost to feats, but failing to meet my expectations. If the number of feats over the life of a character are increased (see my earlier point on feats, then this isn't such a problem, but If not, more need to be available. Maybe you could get 3 feats from your Scheme and gain bonus Expert feats as you level.
The extra skills are very welcome, rogues should have more skills than other classes, but maybe a third skill to really help them fill the Expert role would be slightly better.
(X) Mastery, an extra D6 to certain skills is also welcome and helps fulfil the Expert roll nicely.
Distract seems to be a waste of time that will only be used when receiving a very large damage roll. Giving up your Reaction AND your next Action is to costly. Just make it a Reaction to half one damage roll and you still get to keep your next action. Rogues already have the lowest Hit Dice so offering a good defensive option isn't to bad and doesn't stop a Rogue getting pounded on when surrounded as they can only apply it to one attack.
I have currently only reached lvl 2 so I have yet to test other mechanics.
The rules are shaping up nicely, but certain things really need attention. Skill and feats I would say need the most work. I think its time to drop the idea that feats are optional. Several of the classes important features are now covered by feats (rogue abilities) and so are many basic combat abilities (Bull Rush/Charge). Feats are now a requirement so still having them as optional is nonsense. Skills still have to many to choose and many ridiculous ones. Condense them down and cut out the nonsense (Break an Object)
I look forward to the next playtest and will provide another review when I have chance.