Fun strategy game but very complex and requires attention. It is a very long and almost endless game. 100 or 200 hours is nothing here. Do you know the never ending jokes about Dota 2 and Civilization, how time flies without you noticing or how first few hundred hours are merely an introduction? It's similar with Battle for Wesnoth, although, not that extreme.

To me personally, it is one of first games that introduced me to strategy and turn based games genres overall. Before BoW I hated and avoided strategy or any kind of turn based games. Throughout time while I played it, I developed quite a rough love-hate relationship with this one. Many times of losses, even more times analyzing my own mistakes and learning what did I do wrong.

Content: BoW always has content. Since it's a freeware project that is always work in progress, the quality of content and difficulty throughout the game vary wildly, and there's always something new coming up. There are dozens of playable races and fine variety of campaigns. Some campaigns are trash, others are almost masterpieces.
By playing campaigns alone you will spend at least 50 hours trying to beat them all. If you're tired of official campaigns and want something, there's also modding community, but that one is even more niche. Quality of content can vary even moreso.
There's also multiplayer mode, but it can be rough to play because if you want to play it, you need to find people who want to play with you and make account on official site in 1st place, and after you make account, you wait until your account gets approved.

Gameplay and difficulty: Overall BoW is quite complex. The tutorial you're given is trash. Even if you complete it, you still won't get basics covered.
To get your basics actually covered, play first 2 campaigns- "Tale of Two Brothers" and "Heir to the Throne". They focus on new player experience.
There are lots of mechanics that filter people and make game easier or more difficult (depending on situations) that the tutorial doesn't cover at all. Throw feces until they stick won't get you far in this game. You have to learn mechanics yourself or you'll get filtered by the game and screech like the rest of them. Such examples are:
-How each race reacts to time of day and the terrain (e.g. orcs, trolls, and goblins get stronger at night, or dwarves are stronger on mountains)
-Unit match ups (some units are faster than others and can counter attacks more efficiently)
-Unit leveling (e.g. which units suck at start but become strong later on)
-How to spend turns efficiently
Some campaigns can be easy even on hard difficulty, while others can be a tough nut to crack. Some are very forgiving, while others can be unforgiving and victory can be seen as utopia (e.g.Northern Rebirth campaign is one harder ones to play due to very unfair disadvantages, in which you are given measly weak characters to run against strong ones, and campaign generally focuses on running big squads of troopers).

Soundtrack: Despite that it's freeware project and being done entirely by volunteers, the soundtrack is pretty good. Music fits the game thematically. BoW is mostly set in medieval times, so it's all symphonies of various traditional strings, brass, percussion, and ethnic instruments. You won't find any synths, loops, or rock/pop instruments.