I'm almost done with Season 2 (only have the final episode left). It's enjoyable, but clearly doesn't have the vitality of its predecessor in a way that feels archetypically S2-ish to me. It struggles in trying to maintain the relative believability and tightness of S1 whilst having to deal with a way bigger, floppier storyline. Growing pains, basically, which seems thematically appropriate. You get the impression that a good number of the specific elements that went down well are just being remixed - so you have another D&D analogy, another cutesy phrase for Will's problems ('Upside Down' > 'Now Memories'), another puppy love angle, another vaguely sociopathic cool guy who'll get rehabilitated, the crayon tunnel map instead of fairy lights, etc.
But, the writers/actors and the audience know the characters and scenario better, so there's less need to durdle about establishing things, and more opportunities to land dialogue and character development moments, both of which I think are done well. It feels like there's a deliberate effort to include charming little character interactions (especially with the secondary characters) as a counterweight to the increased scale and less personal feel of the main storyline, which is effective and does inspire some confidence that the writers are aware of the need for balance going forward.
Overall, it feels a bit like they're trying to hold onto everything that was good about Season 1 AND escalate it along every axis, and you can't really do both. That tension has been navigated pretty well for these nine episodes, but the next batch will definitely be a test. S3 will either need to re-compress with a spookier, more intimate angle (unlikely) or go all-in on expanding the universe, and hope that it works. It feels like history would warn against that, but if you want to keep the characters (which I expect they do, since the fandom is there), then probably you have to risk it.