Both series center around a boy in a world filled with monsters, but the main difference is that their stories and interactions are presented completely differently. They both function as kids 'monster of the week' series but Pokémon is filled with epic battles and plots about evil teams wanting to take over the regions. In contrast, Youkai Watch is a pure humor anime consisting of multiple skits per episode with no real plot or purpose. That is not to say Youkai Watch is good or bad, but if you're expecting an epic quest or any overall plot, you'll most likely be disappointed. The series is about Keita's daily life and interactions with youkai, plain and simple. Occasionally there will be plot but it's few and far between.
The anime tends to follow the same structure as the episodes go by, but the series manages to keep most of the jokes refreshing. Some jokes can grow stale but it stays entertaining for the most part. The humor is mainly self-aware, it's a series that is aware that the premise and characters can get ridiculous and embraces it. As such, the jokes can rely on slapstick humor and ridiculous circumstances. For me, the humor rarely fell flat though that will possibly not be the case for you. Still, if you're looking for such a light-hearted humor anime, this may be an anime worth considering.
Another difference between Youkai Watch and Pokémon: Keita, the protagonist, is completely normal. In fact, the only truly unique thing about him is the fact that he can see and interact with youkai. He's constantly referred to as 'normal' and 'average' by his classmates, which I find to be a nice touch to the anime. Keita is more relatable to most children than most protagonists who have something special, a power or being the Chosen One. He's simply an ordinary boy who stumbled upon a gachapon machine by accident.
Even these youkai don't help him out that much- for the most part they just cause him trouble. His 'butler' Whisper is incompetent and knows little about youkai and the series' mascot, Jibanyan, rarely ever wins fights he's summoned to. So really, even his special skill serves to hinder him more than it helps.
He is also not a boy made entirely of moral fortitude and a will to do the right thing like many other kids anime. He can be troublesome and naughty at time, but he can also have many moments of wanting to do the right thing. Again, it serves to make Keita represent an actual child more, which is a nice change from the generic protagonist.
In fact, character is one of Youkai Watch's strong points. Although there tends to be little character development due to it's lack of plot, the characters are full of charm and each character is unique. Each youkai has has their own distinct personalities and abilities which helps prevent the repetitive format from growing stale.
The art and sound are average, typical for most kids anime. It's not amazing but it still has it's own charm.
Overall, I think the series is worth picking up if you're looking for a lighthearted humor anime, or are fond of anime featuring numerous different monsters. Just don't expect any real plot and you'll be fine.
