Steep learning curve. There are a ton of resources out there so even new players can be competitive... the matchmaking system seems rough because most new players get destroyed after their first couple of hours and either quit or take the necessary steps to be competitive.

I'm a new player, and here is my take on what it takes to be relatively competitive early on.

In the get go, you can't treat cards as collectors itms, you have to treat them as currency.

There are plenty of resources, such as icy veins, that can set you up with competitive builds. Using icy veins as an example, you can look at 'budget' decks for each class, as designed by professional players. The playstyle choices will be limitted, but beggars can't be choosers and new players are beggars.

Read up on the different budget decks, pick 1 or 2 you want to focus on, build the basic '0 value' decks for the other classes. Shard everything else (or at least shard enough to build your 1-2 budget decks.) Sure, that Legendary that blizzard guarantees you'll get within your first few packs might be 'cool' but I can almost guarantee it isn't going to 'fit' into any kind of meaningful deck you'd be able to assemble at this point. You'll get a lot more value and enjoyment out of dusting it.

Now you have a competitive deck or two that you can focus on mastering, all within the first day or two of playing the game. From there you can start focusing on expanding your collection and working towards personal goals.