The Tyranids are out and the gaming community is quite polarized in terms of it either being total utter garbage or thinking that "it isn't so bad." Well, having played Tyranids competitively since before the year 2000, back when 2nd edition was transitioning into 3rd, I think I know a thing or two about how to play/win with Nids and why they were so good before and why they are so bad now...Yes, I believe the new codex is so utterly and completely bad I wand to scream and below are the reasons why I think GW totally and completely got Nids wrong-AGAIN.
This is my take on why nids struggle in 6th and why the past few books have been bad and possibly why GW just doesn't "get it" when making new army books for certain armies...
For starters, Tyranids were my first army and I started playing them back before anything had a proper codex when 3rd just came out (the 3rd BRB had army lists for every army to build stuff from). So I am no stranger to 40k or Tyranids.
That said, I saw Nids go from an army that can handle any other army and do well to a codex that just pales in contrast to just about every other one and one that will be hard pressed to win any competitive events.
One of the biggest problems Nids face now is that they were always a close combat army at the core and as assaulting has become less effective, Nids in general have also become less effective. There is a direct correlation between how powerful Nids have been and how powerful CC was in each edition (just like with Orks).
Furthermore, Nids rely on cover and terrain to get by and get in close to deliver their shooting and charges. With the changes to cover and terrain, thing are just easier to shoot dead than ever before and with Ignores Cover being SO prevalent now (which is a GARBAGE game mechanic to have so readily available for so many armies), Nids just lack the survivability to get in close where they want to be.
Therefore, an army that has always been a consummate close combat army that now has to compete in an edition where combat is of minimal import and where an army that has traditionally relied on cover and terrain where both are either meaningless or have a very limited utility...Tyranids are hamstrung from a very fundamental level and need some extra rules or oomph to compensate for these limitations and inherent weaknesses.
Certain rules that will make CC units fast enough or resilient enough to reliably get into combat and effective when they get there are essential for an army like Tyranids. The previous and current codex simply do not have rules or stats in place to facilitate this.
Furthermore, since we currently play in an edition where shooting is the primary way to remove units and cause damage, Tyranids needed effective shooting options to compete with other armies but they simply don't. For example, their ranged anti-tank is virtually non-existent because Hive Guard, Zoantropes and the limited number of shots from a Tyrannofex/Heavy Venom Cannons either can't be spammed to the point of being effective or have too short a range. Don't get me started on their complete lack of reliable AA!
As an example, an army with just 1-3 Las Cannon shots will probably not kill more than a few vehicles in a game compared to an army with 6-10 which will prob kill a much greater number of vehicles (bonus because those armies likely have access to Prescience which Nids don't have access to). Nids simply lack the number of high strength shots at a decent range to take out opposing vehicles which will be able to kite anything with a gun in a Nid army. Furthermore, NOTHING in a Nid army has skyfire except for the Flying MCs and even then, the only options are a Flyrant with S6 shooting (laughable against most flyers) or a Crone which is a flying paper bag of flaming dog poop that has more survivability issues than Steven Hawking in a UFC match...
As I mentioned above, Nids are primarily a CC army in their core army design so their shooting must necessarily be mediocre to compensate for their awesome CC focus...however, since they are no longer the CC army of doom they used to be (Stealers used to just flat out ignore armor for crying out loud!) and how CC is weaker in general this edition-Tyranids really should have had their shooting capabilities buffed to make them able to hold their own against other armies absent any buffs to survivability/CC that they still sorely need and didn't get.
Therefore, the failure in the new codex is multi-faceted because since the "design team" was building the army on a faulty foundation, the structure and meat of the codex must necessarily have problems as well.
1.) Nids needed buffs to resiliency in the form of improved stats/saves or rules to ensure they can get into combat or range to do something other than die horribly. They simply did not get them.
2.) Nids needed better shooting to have a way of meaningfully dealing with Vehicles at range as well as SOME way to deal with flyers in a meaningful and reliable way. They simply lack any way to handle flyers outside of a few overpriced and underpowered units.
3.) Anything that got "cheaper" didn't actually get cheaper...they were either waaay overcosted to begin with and finally got priced to what they should have been in the previous codex (and should actually be cheaper than they currently are) or the upgrades necessary to make them effective went up in points so they actually got more expensive.
4.) Some things either stayed the same points cost or got more expensive for no good or justifiable reason along with nothing being done to address glaring problems in their stats, rules, utility or effectiveness.
With all of that said, nids are a failure now and it's really sad because GW could have done so much with them (and every other army TBH). We are able to overlook the failures of certain other codecs because they have many varied and playable units/builds. Nids have none.