You need to have seen other generic isekais before because this is a parody of the genre. Here, there are no messages, no great speeches, no ideas, nothing of this sort. Instead, you'll find fanservice, lewd humour and immature gags.
For S1 and S2 and the OVAs:
Konosuba is very light-hearted and with nearly no stakes at all because of the literal deus ex machina. It's an anime where no one dies. Moreover, the evil guys aren't really evil, and when they suddenly become so, it's not as impactful. Meanwhile, all the good guys have a tremendous explosion resistance. The protagonists are not "useless" or "weak", contrary to what they will say : they are just very unmotivated and their powers somewhat flawed.
The team is your average RPG squad, except everyone is crazy in their own way :
Aqua, being the dumbest character ever, impedes the progress of everyone by crying and complaining, and causes nearly all their problems because of her dumbness, while being totally the most OP when she is motivated;
Darkness, a knight refurbished as a tank, and the most developed character by far, except it's only the fanservice;
Megumin (best girl), is a mage but with one spell slot, and the only really motivated character;
Kazuma is a jack-of-all-trades generic protagonist, and is there just for fun and jiggles, and there are enough jiggles to outgainax Gainax themselves.
There is nearly no character development : Megumin and Darkness are developed ONLY at the beginning of the second season, while Aqua gets some at the end (yes everyone else including Kazuma get NO development). They all stay like the gimmick they were defined as in their first appearance, except Aqua who gets more serious for no reason at mid-S2. It would become (it becomes) really unnerving if there is no development, but fortunately new characters appear.. which are far more bland and useless.
The worldbuilding, even for an anime that short, is below the ground. It functions like a videogame world for many matters and purposes, but it isn't : The magic system is mana-based and contained in a skill system : Only Aqua and Kasuma acquire skills during the 2 seasons. Everyone is either practically invincible or can be revived. For the rest, it's standard medieval-fantasy with nearly only humans (and liches that behave like humans).
The scenario progresses somewhat steadily, alternating quests probably found in Monster Hunter and your average fantasy boss, but in less cool. There is no cool factor in this anime, because it has all been subverted, for "humour", except the humour is the same jokes for 20 episodes (+2 OVA). Darkness is funnier than everyone else (at once) because she is masochist, and it works only because she is practically invincible.
The art and the OST is average, with cool themes, great CGI for bosses and for Megumin only, great animation : the animators were as lazy and Aqua and many things that should have been animated aren't (after all they spent all their time animating boobs...). The cities are great generic landscapes, but the wilderness and the dungeons are subpar.
If you want to watch this, turn your brain off, have watched generic fantasy animes beforehand, because this is the only way you'll get to enjoy this. It's not deep at all and it's as hollow as Aqua's skull. (and forget the first OVA except if you want more fanservice)
