Well at first I was thinking the codex was rather bad till I actually read it. It have some better options that simply wasn't there before. In my opinion I would say in some ways this codex is better than the last, won't go as far as to say better than 4th nids.
Anyway the nids needed to be nerfed in some areas and was buffed in some. Since I want to stay positive I want to hit the good. I might mention negative a bit, but my main focus would be the units I liked or stand out. Anyway if I didn't mention a unit I thought it's negatives out weighed the positives.
Before I begin since there are so many reviews about the codex I want keep reviewing what has been said already. However I may repeat some stuff, but will focus on the good.
Hive Tyrant:
After looking it over I would say winged is your best option here. Honestly if you want a walking Tyrant you should just take a Swarmlord. With 2 powers you have a 50% chance of getting warp blast which will help a lot with anti-air. Speaking of anti-air this is the only real viable model for ant air in my opinion, the goal is to shoot flyers in the rear.
After looking at the weapon options it seems that 2 twin devourers is your best bet. Sure you can take melee weapons, but this option with increased bs is really too good not to take. Another nice option is the Thorax. The Thorax gives you a flame template which can be of 3 types. Personally I would opt to go with the strength 3 template with shred and rend that can do some good against hard targets. The options of switching through 4 weapons is nice. You can shoot 12 times, flame and shoot 6, drop two templates, etc.
Miasma wouldn't be a bad option, but I think it wouldn't really be a good one. However you can possibly have 2 flame weapons that wound on 2s which you can switch from shooting 6 strength 6 shots 2x., not to mention following up with vector strikes.
Besides the options mentioned. I think taking hive commander would be a good one to take. All I can say is remember Tervigons can be troops and they now spawn gaunts after they move. Which means you can have two units outflanking instead of one.
As a note I wouldn't suggest running two winged tyrants. It seems good, but you should consider your other HQ options. However running two winged tyrants is not a bad ideal.
Swarmlord:
Besides being really expensive he does a lot. As a master 3 psyker he have a good chance of getting really useful powers you will need. I would say take bodyguards with him to keep him alive and hopefully you pull out fnp to help keep the unit alive.
The main reason I would take him is due to MC shooting or Preferred enemy which some units can benefit nicely with those types of buffs. Also getting your guys in on a 2+ reserve roll due to him is very helpful.
For the most part he support your army and if anyone is foolish enough to get close he will kill most models in combat. However unless you running a lot of reserve units I wouldn't run him.
Tervigon:
All I hear is complaining that the model is more expensive. In all actually it is cheaper. It's cheaper since you are not taking max psychic powers and one or two weapon options to hike up your gaunts. You can look at itas more eexpensive since you don't get what you use to get for a little less. Anyway I still see reason to run 3 still in your army.
First off you might have to run this guy as a HQ option now. Taking 30 gaunts to one tervigon is not super cheap. Remember you are paying 30 LESs points for a full squad of 30, but you are paying an extra 230 points to field 3 tervigons. To get around the price problems you may have to run them as HQ instead. I would say two as HQ with one as a troop would actually get you the same as before, but cheaper. I know you losing anti air options if you do that. However I plan to probably run one as HQ with two as troop to cut in cost. From experience 3 works well for me.
The good thing about spawning after you move is that you can easily get full movement with your Tervigons., before you would lose movement due to moving your tervigons after you spawned everything. Now it will conjust your army a little less. Also you are saving time by moving one model than spawning, instead of spawning a bunch of models and than move them foward. They can still shoot and run which is good.
The only upgrade I see taking is the flame template weapon. Got to love a rending shredding flamethrower.
Looking over troops you only really have Tervigons and gaunts again. On the bright side devil gaunts are much cheaper and you can outflank them if you take a tyrant or try to get them to come through a Trygon tunnel.
Lictors^:
They are surprisingly better. You have options and can actually use the trail ability.
You have the option to infiltrate them. The good news is you can disrupt scouting armies, like they would scout up any way against nids. Anyway you can cover a distance of 12" from your 18 " and be able to accurate deepmstrike a model 1" away from a target, Mawlock anyone.
The good news with proper terrain placement you can get 2+ Cover saves easy in area terrain.
In a pinch you can get behind or near artillery vehicles and shoot them in the rear or assault them and rend them to death.
From my experience you usually wind up gtg a lot and get the other army to stop shooting your other bugs. In a pinch you can fire your flesh hooks with snap shots.
Zonathropes:
Helps with synapse and also helps with psychic love. One of the few models with two psychic models. You either warp blast or use a support power pretty much.
I think this codex edition really will encourage you to run a lot of zonathropes. I would say two squads would be helpful.
Hive Guard:
You need vehicle killers and cover denial weapons, they kill pathfinders dead. For the like of me I fail to see why you will pay more for a worst weapon. If 13/14 armour is out there your Zonathropes or MCs can deal with it.
Fast Attack:
So much to be said for this slot and so little. Basically I personally like spore mines even more, although screwing up deployments was nice. Before I go further I looked at both flyers. Honestly you just Better off with winged hive tyrants. Anyway if I would run fast I would probably run the mines. Besides that your flyers besides vector striking really doesn't do much and can't really deal with other flyers. They not bad, but unless you really want a nid air force I wouldn't bother.
Going to the mines they are great for several reasons, only reason I would run a harpy or Biovore.
1. You can move them in 3" in any direction and assault at half range. The good thing about this is before they would randomly just be on the board. Now when they assault and blow up you are actually getting a lot of models in the explosion.
2. They screw up over watch. What you do is keep them near units while you advance up. The enemy have a choice of killing them or shoot at the nids pushing uo. Once you can assault with another unit make the decide rather if they want to shoot the mines or the gaunts. Personally I would assault with the gaunts first and than the mines. I personally think the mines would do more than regular gaunts in combat anyway. Also who cares if you blow up your own guys.
I think with tervigons, Biovore, and harpies you can cause over saturation and cause your opponent difficulties. You can potentially pump out 9 units a turn on top of what you already have. Quite frankly I think this is a huge strength in the new material. To be able to control where the bombs go help mitigate overwatch a lot. Also you force your opponent to waste shots at free units. I mean in 3 turns you can have 27 extra units on the table. Oh I forgot you can pump out 11 due to 2 tervigons as HQ, so 33 extra units in 3 turns.
Trygon Prime:
This guy can shoot 12 times and drop a flame template that wounds on 2s, not to mention you can control mishap a bit, if swarm lord blesses this guy than he can 're roll 1s to hit and wound. Besides being shoot like your hive tyrant he is a good melee monster and also give out more synapse.
Mawlock:
I actually hated last edition Mawlock and felt I had to take 3 to make them really viable. Now you telling me he can use his template twice on a target, come on. If you didn't kill them the first time you will probably do so the second time. If you mishap it is a joke since you can go back in reserves or actually do yourself a favor and set up another ds attack next turn. If you roll a one it dies, but you probably earned back its points when you hit your target.
All that being said. I think it's more balanced and in many ways better. However I wouldn't use it as a vehicle killer though. For starters think about landing on top of O#Shova and his friends with this guy or that annoying group of broadsides. I really think the Mawlock is almost actually an auto take option now.
Exocrine:
Basically an accurate Mawlock that can't deny cover. However it is great for dealing with other armies MCs if they are stupid enough to get within 24" of this guy.
I think it's a great model, except the range makes it better than ok. Anyway decent player would blow this guy away. However if you have 3 of these guys it forces you to either kill them or the advancing troops. If I decide to use one I would probably use 2 or more. If the other side have no MCs it than comes across as a waste of points to me.