Kind of off-topic (or at least focused on one element), but I don't get this focus on assault grenades. The same thing applies with khornate daemons, and whilst, yes, I'd love them to have them, I'd argue differently;
~ If every army has assault grenades (which, if daemons and bugs get them, they pretty much do), then why bother with the assaulting into cover rules at all?
~ The whole 'defending a barricade' thing is sufficiently iconic that the rule of cool says it should stay in and therefore have a game effect. Equally, if I'm buying an aegis line, it should do something whether I face an assault army or a shooty army.
~ Striking last for one round of combat isn't inherently a big deal. Where chuckles (quite rightly) points out that it is, is for units which will strike first in subsequent rounds, essentially increasing the number you lose before you get to start killing things.
~ This is true in several parts of the rules, though. A pure assault force charging at a gunline can now experience an extra turn of fire (as rapid fire weapons can shoot at full range whilst falling back), plus a not-quite-extra turn of fire from overwatch.
~ This doesn't make assault grenades a 'must have' in my view. The problem with not having them, boiled down to its basic level, is "I have lost N extra dudes before I get to attack in round 1". Is it not therefore workable to allow the squad to be N dudes bigger for the same points cost?
~ This works better in my mind as, depending on the scale of cost drop, it (a) covers off the problem of overwatch and moving rapid fire, and (b) the biggest losers of the new ruleset (purestrain genestealers) are due a points drop anyway for not being able to charge from infiltrate or outflank. Their costing more than marines doesn't make sense anyway - tyranids and warrior daemons are, as noted, supposed to be this massive, slavering horde...
Most of the rest is fine. Yes, all right, overwatch casualties coming from the front can in theory stop a charge, but with fleet-rerollable 2D6" charge you get a few inches further on the charge anyway. Precision shot is largely pointless against an army with few special weapons or squad leaders, and whilst krak grenades hurt, being able to challenge power-fist wielders and step on them in person more than makes up for it. The AP3/AP2 close combat thing is largely irrelevant as most tyranid armour-piercing close combat attacks go through anything anyway.