I don't expect perfection, but the challenge rating system was the opposite of helpful. Ideally, it should give me a broad guideline for threat levels but I found that it fails to do so miserably.
Again - this is a fool's errand. I can build encounters that are a horrible challenge for one party and trivially easy for another. As an example, imagine a party that has no ranged attacks beyond 120 feet. Then imagine another with archers are long ranged spellcasters. Put them up against manticores out in the wild with the manticore tail spikes firing at 100/200 range. The PCs that lack the capacity to attack at 120 to 200 are going to find that hard, regardless of level, while the long range PCs level 4 and above will likely not find it very hard. The game is too diverse to have a system that broad guideline that is effective.
I do like combat in D&D, but it's not exactly a speedy system, and when you have multiple lower difficulty encounters that don't really matter they become tedious slogs. ...
This is what I am counseling against here. Saying that a battle that doesn't threaten the life of PCs won't really matter is undervaluing the importance of story and the other ways you can challenge a PC. Some of the most iconic battles in my campaigns over the decades involved the PCs trying to stop someone from doing something - and the only attacks that were lanuched at the PCs were things intended to slow them down or cut them off from their goal - not kill them. Battles are tedous when there isn't an exciting story behind them that pulls the players into the action. Often, the most tedious battles are those where two forces have no objective other than just to kill each other.
Deadly challenges, battle after battle, are boring - and in truth, are either 1.) lies or 2.) end up killing the PCs off quickly. If the PCs are not dying, then the battles are not truly challenging because there isn't a real risk of failure - or the DM is saving the PCs by pulling off the throttle which ends up meaning that the PC actions have no value or merit ... the DM is actually dictating how things will go. If they are real challenges all of the time, and the DM is not protecting the PCs, then PCs die a lot - and you'll get a TPK eventually. All of those options are problematic. Further, it ends up making the heroes of the story, the PCs, feel like they're being bullied rather than that they are the heroes of the tale.
The #1 indicator of a good DM in my eyes is the ability to make an exciting game that challenges players and PCs in a variety of ways.