Before Guzma we had Lysandre and before Lysandre Pokemon Catcher without a coin flip.
Guzma is a great example of a good ulitiy supporter. You don't need any conditions to play him, nor are you bound to a specific type of Energy / Pokemon to benefit from him. He's versatile enough to be played in every deck, yet situational enough to almost never be run as a 4 off, no matter if you have access to VS Seeker or not.
What I really like about the card : he isn't used for the same reason in every match. Think of another utility supporter, lets say Team Flare Grunt. The reason to play the card is pretty obvious in every imaginable scenario. Now, if we talk about Guzma, the first thing that pops into our heads is to simply snipe a bench Pokemon. However, I frequently use Guzma to switch out my own Pokemon (maybe to avoid a revenge KO, or because I set up a Pokemon on my bench). I also use it to get rid of an active Pokemon with an annoying ability (Trevenant, Glaceon GX, Wobbuffet, etc.). You can also try to trap a high retreat Pokemon on your opponents side, or use it to attack multiple turns in a row with a card like Ho-Oh GX, etc.
But, without a doubt, the best thing about this card is that its mere presence changes the way we play the game. When your bench is vulnerable and can be targeted at any moment, you are going to plan your turns accordingly. The Pokemon TCG only has limited interactions between players, compared to other TCG/CCG games and a lot of the time it can feel as if two goldfish were playing against each other, since the majority of your actions are done in your own little bubble. Cards like N and Guzma force you to consider further actions from your opponent, as blindlessly running into them will often result in your demise.
The shadows of the abyss are like the petals of a monstrous flower that shall blossom within the skull and expand the mind beyond what any man can bear, but whether it decays under the earth or above on green fields, or out to sea or in the very air, all shall come to revelation, and to revel, in the knowledge of the strangling fruit - and the hand of the sinner shall rejoice, for there is no sin in shadow or in light that the seeds of the dead cannot forgive...