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Launch one really was a comedy of errors in the launch platform.
In launch 2 the booster did exactly what every other booster by everyone else (except the falcon 9) does. Got it's payload to the target altitude before separation.
The second stage reached space.
The N1 platform didn't do any of that.
You have no idea what a testing platform looks like, and are too used to NASA one shot rockets that cost 3 billion each just to make sure nothing goes wrong.
This sounds wasteful on paper, but in practice it is much much faster and amazingly enough cheaper. With traditional rockets you never make enough to enjoy economies of scale, but with SpaceX's approach they've dropped the cost of the engine by about an order of magnitude over just a few years, and it was already a very inexpensive engine. For the cost of a single RS-25 you can buy 400 Raptors.
The second stage exploded as well, possibly because of FTS, possibly not (was it ever confirmed?).
SpaceX clearly has a winning method, as they have a success rate of 99.3% and hold the record for most consecutive successful launches at 253. Second place is Soyuz-U, which had 112 consecutive successful launches and an overall success rate of 97.3%. SpaceX has more consecutive successful booster landings (173) than any space program has had successful launches.
It exploded while attempting to test its landing maneuver. If it just turned off the engines and dropped itself into the ocean like a normal booster, it likely would not have exploded (for one thing, there wouldn't be any fuel left in it being saved for landing).
A few people have slosh modeled the booster flip around duplicating observed speeds and accelerations and surmise the following. The flip around was too rapid causing slosh to one size of the booster. In addition there was negative acceleration that would have allowed the remaining fuel to experience zero gees pulling it away from the bottom of the rocket. When the engines fired back up it would have hit the bottom of the rocket with something between 20 and 100 tons of force. Based on SpaceX description, the FTS was not used.
The second stage at least appears to be oxygen leakage. The graphs shown on flight day started showing a more rapid depletion of oxygen after second stage lighting. SpaceXs language was something like 'flight was unable to reach orbital insertion and was terminated, pointing to the FTS being used.
Multiple iterations of test flights that are expected to fail is a much faster way to develop impressive tech than spending 3x longer doing on the ground analysis of every detail of everything because you can't bear the PR hit of something that can be painted as a failure.