Here's my further thoughts after playing a roughtly 400 point game with 2 squads of infantry (2 USMC and 2 PLA)
The new action, reaction, suppression system is great and adds a lot more to the SST system. Just like the original SST rules, there is a lot of interworking between the rules that leads to a lot of tactical depth despite how simple the rules look. This time around, however, it's a lot cleaner. There's still some areas of question, but less so than SST.
The game is pretty lethal to units out of cover, but not always with bad rolls. Likewise, it's difficult to kill units in cover, but sometimes you get those amazing rolls. The average infantryman has a target of 4+ with a kill of 6+. In cover that goes up to a target of 6+ and a kill of 8+. So units in cover can sometimes to hard to dislodge, but will a full squad firing, including special weapons, you can usually kill 1-2 units with a decent roll a turn. What tones down the lethality of the game a bit from SST is that each model only has one damage die instead of 2, and the suppression system.
The game revolves around suppression, which is a good thing. Almost every squad in the game comes with an MG which is vital to suppressing the enemy. Shots from the MG count double for suppression and using an MG fireteam is a great way to suppress the enemy enough so that you can move forward. Not only that, an MG deployed with a ready action has 4 damage dice counting for 8 suppression, that's almost an entire squad worth of suppression, add a rifleman and you can suppress a 9 man USMC squad.
An example: It's late in the playtest game and the USMC is sweeping up the last of my PLA. I have fireteam in a good position encircled by cover with a deployed MG and two riflemen lying in wait for a flanking USMC squad of 5 to round the corner so they could react. On the previous USMC player's turn he had managed to move a lone MG up into cover with LOS to my fireteam. He activates the lone MG first, deploys it, then shoots at my PLA fireteam. Since they're in cover, he doesn't get any hits with poor rolling, but since he's got 4 damage dice turned into 8 points of suppression, my fireteam of 3 is now suppressed. I can't shoot back as a reaction, only move, and I lose one action the next turn. The USMC flanking squad moves out of cover since I can't react to shoot at them, and shoots with their second action. They kill two riflemen and suppress the fireteam again. Now when it comes back to my turn, my lone MG has no actions to do anything and on the next USMC turn he's quickly killed.
The USMC squad is nasty against infantry. They excel while in cover and shooting at distance. With a range of 24" and the ability to negate one point of cover means that the basic rifleman can do as much of the killing as the SAW or m204. Their armor of 5 helps those riflemen survive long enough to shoot. In general, the basic rifleman for the USMC should not be used as just soak units, instead suppress with the SAW, move up the riflemen and m204 to get the kill. Their only weakness is the lack of a d10 damage weapon. They don't even have the option of taking such a weapon for more points, thus in the basic game they have to rely on their own tanks for anti tank support. They also need momentum on the attack, keep the enemy suppressed and don't let up. Since enemies tend to outnumber the USMC fireteams, it's important not to let the enemy get a full turn of shooting at your troops or the loss of just one or two will really hurt, not to mention the suppression. The special ability of intelligence reports can help obtain this momentum by allowing you to reroll the deployment and first turn die.
In my playtest game the USMC player failed both his deployment rolls, alowing me to go first and fire almost an entire squad at him. Eventually that momentum allowed me to kill off the squad completely.
As for the PLA infantry squad. Well they rely on their numbers, cover, and the slightly better mobility. The PLA squad has no armor, so if a model gets hit he's dead. The move score of 5" helps them get in and out of cover, and the slightly larger squad size means you can soak a few more losses. The biggest strength of the PLA squad is how much raw firepower they have. They have 2 MGs and on top of that they get a rocket launcher, plus they can divide into 3 fire teams. The two MG teams really help with suppressing the enemy and making sure that you arne't being shot enough to take serious losses, then the rocket launcher helps deal with enemies in cover, since the d10+2 will usually kill something per shooting action. Also with the larger squad size that's more basic rifle fire.
A fully deployed PLA squad rolls 15d6 and a d10+2. Having the lead team and the rocket team fire while deployed generates 9d6 and d10+2, and that leaves the other MG team to add on more suppression later. It's hard not to kill with that much fire going out, but it might be better to use the MGs on suppression duty to make sure the enemy can't shoot back enough to exploit your troops' lack of armor.
Oh, and a note on deploying troops and moving them around. Since the highest damage dice are applied to the models closest to the firing unit, it's okay to have more valuable units behind the front of a squad and out of cover. They still get an obscurement bonus against incoming fire from the front, it's still bad if your opponent gets a good roll, but there is no saving yourself from that situation anyway. Also, models within a unit do not block line of sight to each other, so there's no worry about LOS, the only issue is range. This is a pretty important rule for the PLA since they have a lot of basic riflemen and rely on their special weapons. The basic riflemen in front often use up the cover.