Went to my local GW store today and they had a copy of Space Hulk to prepare for the September 5th release. As a result, I was lucky enough to play the game and understand the rules, both as Space Marines and the genestealers.
The game mechanics are similar to the 1st edition with a few (important) additions.
The Space Marines have 4 action points (AP) and the genestealers have 6. Space Marines can also randomly pick command points (CP) (from 1-7) to add to any actions during a turn. They also have a time limit of 3 minutes to move, shoot and complete their entire turn! The genestealers have no such time limit.
It takes 1AP to move and fire, open a door, turn 90 degrees and start a close combat action. It takes 2AP to go on overwatch and this enables the terminators to fire at a moving genestealer (during the genestealer turn), once for every square they move. It also takes 2AP to move backwards one square.
Storm bolters roll 2D6 and kill on a 6. If the terminator stands still and fires (sustained fire), the second shot kills on a 5 or 6. Bulkheads can also be destroyed on a 6 although the chainfist can automatically destroy a bulkhead for 1AP.
The terminator armed with the heavy flamer is one to protect since a number of missions require rooms to be set on fire. The flamer template is placed on a tile and also ignites every square around it. This can kill genestealers on a 2+ and remains on fire until the next Space Marine turn. Very handy for limiting genestealer movement but the ammo is limited to 6 shots!
The thunder hammer is great rolls 2D6 and forces the genestealer to lose 1 attack. Similarly, lightning claws roll 2D6 +1. The standard attacks for terminators in 1D6.
Similar to overwatch, terminators armed with close combat weapons can go on 'guard' (for 2AP) which means they can force genestealers to re-roll one attack.
The genestealers have 3 attacks in close combat and whoever scores the highest kills the other. The terminator captains have +1 in close combat and can force a re-roll.
The broodlord is stupidly hard - it requires double 6 to kill with a storm bolter and has a similar rule in close combat.
The librarian has 20 psi-points which can be used to cast psychic powers or be added to dice rolls (much like might in LOTR) and is therefore one to protect (but is also one of the only Space Marines who can take on the broodlord).
The game was brilliant to play - the mission we played involved the terminators trying to burn two rooms (which housed barely-alive techmarines which the genestealers were using to breed more genestealers). It is really hard to win as the Space Marines simply because the 'stealers are neverending. The randomness of the blips is good, both for the Marines and genestealers and the game hinges on every dice roll.
I cannot wait to get my hands on it now! Will be playing more Space Hulk over the next few weeks prior to the official release.