This may be my favorite stand alone novel outside the opening few (which I adore). While the whole series is a definitely a power fantasy of epic proportions, this volume stands out in that it documents the rise of Rimuru as a Demon Lord. In this world the class system has two tracks, Good and Evil if you will. The good side peaks with a Hero while the evil side peaks with Demon Lords. Now you could argue that Rimuru is kind of stuck on the evil track of this class system for the most part because he was reborn a Monster anyway, but the Demon Lord status/class requirements have some pretty strictly evil sounding pre-reqs which go against pretty much everything he stands for. The journey to this monumental decision makes for some very interesting and compelling story telling, and I can assure you it is all quite satisfying.
So the content is good... but the pacing is not. And maybe it's not really the pacing as much as it is that the author is not concise in his expansion of the lore.
Prior to reading the light novels I read through the entire web novel translation and they are somehow better paced. Reading the light novel versions, you can tell the author used the publishing opportunity to pour back over his work and expand it quite a bit. This has advantages and disadvantages. If you like the characters and love this world, the light novels really give you so much more to enjoy and sink your teeth into.
I can't tell you how relaxing it is to just sit back and enjoy the antics of the various characters - all of whom I find to be quite likable, while flipping through the excellent printed editions and beautiful art of the light novels.
But the pacing gets murdered by this expansion of lore throughout the series.
For example - Book 4 ends on a MAJOR cliff. Book 5 doesn't pick up on that cliff until half way through the book. It's not that I don't enjoy everything that's being written, but the order is disorienting at times. I'm the sort of person who found myself hating Frodo because he kept interrupting what was going down with Aragorn. It's not that Frodo's arc wasn't interesting, but Aragorn was where the action was and the cuts to a much slower paced section of story always devalued that slower paced story for me. (Lord of the Rings reference)
In the original Webnovel, the storytelling was always pushing forward and progressing with Rimuru front and center and I think I prefer that. Still, the added content is all quite entertaining and enjoyable, so I can't be too harsh on the extension.
All in all, if you like the characters introduced in Vol 1, I think you'll have a blast here.