Even though season 1 stands by itself, there was still a lot of potential for season 2. They could've ditched the old cast completely and bring in entirely new faces to play new games. I think with compelling characters, it would've worked great. But it felt like the makers were too scared to ditch the fan favourites, and so their presence and screen times were justified by unnecessary and bloated plot lines. Eg: Hwang Jun ho still searching for the island without a single clue. It probably would've been better seeing him enter the games this time and the Front man in turmoil trying his hardest to save him. But no, they played it safe.
Also due to the star studded cast, there were no real stakes in the few games they played. Unlike last season, where we never knew who would end up dead during each game.
Keeping all these aside, the main drawback was quite literally the lack of games. Whole 1st season had packed 6 intriguing deadly games into 7 episodes, this season had only 3. With the 1st one being a repetition. And the music and tone of these games seemed very far from the grim and gloomy atmosphere in the first one.