The Pokemon Adventures manga is a very, very loose adaptation of the first two Pokemon games Red and Blue (or Green if your Japanese).
The first three Volumes covers the Red/Blue era and unlike the Anime it follows the journey of Red, the playable character from the first game and his Pokemon partners Poliwhirl/Poliwrath (Poli) Bulbasaur (Saur) and Pika (Pikachu) on his quest to the strongest Pokemon trainer in the land. Standing in his way however is his rival Blue and the villainous organisation Team Rocket, who actually come across as a serious threat unlike the show and even the game this is base off of.
The main thing to bare in mind whilst reading this is to remember that this is not the anime, this manga follows its own story and has its own take on many of the characters from the games. Red himself is very different from Ash and while there are some similarities he is a very different entity.
Whilst not without its flaws, it is rather dated concidering how far we've come in terms of Pokemon games, and being an adaptation there are some liberties taken such as Poliwag and Nidorino hanging around Pallet Town and there being a Kangaskhan in Viridian Forest, however in the whole it is an enjoyable read and I think anyone who likes Pokemon will enjoy this.