It's pretty well-known that the Tyranid codex is the red-headed stepchild of 5E. Hell, we weren't that hot with the 4E book, either, shitty Nidzilla lists aside. I may disagree on the degree to which the codex has problems (as bad as Necrons? really, Stelek?), but I think we can agree that the problems exist and are major enough to place them well below the other updated books. As of late, it's become popular to post lists of "fixes" for how one would handle redesigning the book to be more functional. This is my shot at that.
HQs
Tyranid Prime: Add an option for Wings for 20pts. Let them get into Spores with their buddies.
Hive Tyrant: Indescribable Horror works on any unit that wants to shoot or charge the Tyrant (only if he is alone.) Hive Commander stacks. Deathspitters on monstrous creatures are S7 AP5 Assault 6 for 20pts. Devourers are 10pts, Strangler is 15, HVC is 20. Psychic Scream is 12" radius and no cover saves. The Horror works on Fearless/etc units. Leech Essence and Paroxysm are 18" range. Thorax Swarm is 15pts, Armored Shell is 25, Wings are 40. Shadow works on guys in vehicles.
The Swarmlord: Invuln is either just a straight 4++ or a 3++ in CC. BS increased to 4.
Tyrant Guard: Boneswords are 10pts.
Tervigon: Onslaught is not a psychic shooting attack. Stinger Salvo is 24" S6 AP- Assault 4.
The Parasite of Mortrex: Either give him a 4++ "dodge" save or make any model he kills spawn Rippers, not just those that fail a test. Alternately, give him a Power Weapon instead of Rending and T5. (In the former case, outflanking units lose a model automatically rather than having to test.) Either he or the Flyrant should make Shrikes and/or Gargoyles troop units.
Elites
Hive Guard: Probably a small price bump, maybe 5pts/model. Hey, you can't have everything.
Lictors: They don't get to assault out of deployment, sorry, that's Ymgarl's schtick. Let Pheremone Trail work when they're off the board or let them come in automatically first turn. Give Flesh Hooks three shots or make them BS4.
Deathleaper: Drop cost by 10pts or give him an invuln in CC, probably a 4++. Flesh Hooks and Pheremones as above.
Venomthrope: Make them T5, give them Stealth, or have their "aura" grant Stealth. The latter seems like the best fix, although it probably necessitates a cost increase.
Zoanthrope: Move back to Heavy Support. While it fits just fine in Elites, there is a need to diversify anti-tank in the codex. A little something to make Warp Lance more reliable would be nice, too.
The Doom of Malan'tai: Spirit Leech doesn't allow cover saves OR affects units in transports but allows cover saves. Probably move to HS along with Zoeys for uniformity's sake.
Pyrovore: Change price to 25pts per model or let them "throw" their templates a distance and give them a survivability boost (3+ or W3). Maybe an upgrade to I2 would be nice.
Ymgarl Genestealer: Grenades. They don't really need anything else.
Troops
Tyranid Warrior: Venom Cannons S7 or twin-linked.
Genestealers: Grenades option (1-2pts), possibly as an upgrade for the Broodlord (i.e. "if I'm here my whole squad has grenades.) Aura of Despair should be used during/before shooting phase so it isn't worthless.
Mycetic Spore: Remove the retarded FAQ changes; Primes can join anyone's Spore, you can drop a Spore empty if you want, and Tank Shocking won't move them (the tank stops 1" short.)
Termagants: Stranglewebs are free or S4. Spinefists are free or 18" range. Spike Rifles are free or 24" range. Giving them a way to glance tanks at range might be nice also.
Hormagaunt: Decrease to 5pts, with the option for Adrenal + Toxin for 8pts. Alternately, make them 7-8pts and Beasts again (losing the 3d6 run.)
Ripper Swarms: Make them scoring. Decrease the cost of all their options by 1pt. Alternately, make them 6-8pts/base instead of scoring.
Fast Attack
Shrikes: 4+ save or 5pt cost reduction. Make their options the same as Tyranid Warriors'.
Raveners: 4+ save (4++ in CC?) or some other boost in combat.
Sky-Slasher Swarm: Seriously, why do these even exist?
Gargoyles: They're fine! Just make a way to have them as troops via a HQ or something.
Harpy: 10pt cost drop and either T6 or 3+ save; or larger (~40pt) cost drop. Give it three attacks and WS4 for crying out loud, MCs shouldn't be atrocious in a fight. "Derp, I'm like a Dreadnought but fewer attacks, lower WS, and your regular guys can punch me to death without needing a Fist."
Spore Mine Cluster: 5pts per model. Let them either do their wacky deploy thing or Deep Strike normally (exploding if they mishap.)
Heavy Support
Carnifex: Drop cost by 30pts or by 10pts and let them take whatever options they want (i.e. wound allocation nonsense.) Change Deathspitter and other gun options as with Tyrant. Give them I2; WS4 would be nice, also. Toxin should be on a 2+ or at least a 3+. Crushing Claws should be +d3 attacks and rerolls against other MCs/vehicles.
Old One Eye: Make him an upgrade to a Carnifex squad. Give him Ld9. Let his attacks chain infinitely, a la Blood Talons. Give him a 2+ save. Drop his cost some on top of all that, because seriously.
Biovore: Let them shoot at targets they can't see while Lurking. Maybe also a small price break of S5 on the hits.
Trygon: Let units pop out of his hole the turn he arrives. Alternately, treat it as a board edge when entering (so they can move full distance and potentially assault.) Let anything except flying critters arrive by the hole, because if it's big enough for this 8" tall "everything on the board has LOS to me" monster, I'm sure a Huggafex can fit through.
Mawloc: Give him two sets of Talons and WS4. Also, give him Fleet. Why fuck doesn't he have Fleet? Don't allow cover saves against his Terror from the Deep rule. Make it so he can't mishap on terrain. Hell, make it so he ignores terrain when he moves; dude is burrowing, right?
Tyrannofex: Make him 210pts instead. Or make the Fleshborer Hive and Rupture Cannon be additional fire modes for his main gun (a la the Soulgrinder), not replacements. Or make him BS4 (or twin-linked) and ~20pts cheaper. Throw in another small upgrade as well (T7, WS4+Scything Talons, an invuln, whatever.)
Overall
So what are we adding? Anti-tank options across the board. Price drops on the MCs to even them out with all the extremely cheap tanks out there. Opening up some of the obviously-shitty options. Enabling reserve builds. Enabling swarms of little bugs. Giving the army a couple long-range options they don't have to pay through the nose for. Making the special characters actually viable.
What aren't we doing? Letting the whole army assault the turn it arrives. Making everything mega-cheap. (Cheaper, yes, but 100pts for a T6 body is a ridiculous deal.) Making any of the options for armor-ignoring CC attacks cheaper than they are or giving armor-ignoring ranged attacks, which are out of theme for 'Nids. We also aren't making the "good" units any better at what they do, because in most cases those guys are just fine; the point is to shore up the units that are missing things.
