1 The game was a breakthrough back then
When Chrono Trigger was first released it was considered by many a great game compared to the games that were available back then. As technology advanced and more games showed up some people started believing that Chrono Trigger is no longer good compared to those games.
2 Chrono's personality wasn't appealing
Many people didn't like Chrono's personality. Some said that he didn't have a personality or seemed more like a robot.
3 The story becomes interesting later
Some people didn't like the fact that the story doesn't get really interesting until later in the game. This could have made some people stop playing the game before reaching the more exciting part.
4 It's no longer original
When Chrono trigger was first released it introduced many original ideas that were later copied by other RPG makers. Some people who tried playing the game years after it got released weren't impressed as those ideas seemed old.
5 The characters aren't serious enough
Many people failed to develop emotional attachment to the characters as they didn't look serious enough or didn't have that kind of serious personality. (See
Why Final Fantasy 6 is overrated?)
6 The game is short
Some people didn't like the fact that game is a bit short compared to other RPGs.
7 Very high expectations
The fact that many people try to play the game with very high expectations, as a result of the fuss surrounding the game, has resulted in so many disappointments when the game fell short of those expectations. (See Why is The Last of Us Game Rated 18+)
8 Dungeons are boring and depressive
Some players didn't like the fact that dungeons were usually dark, boring and a bit depressive.
9 Enemies are boring
Some people didn't like many of the enemies in the game and considered them to be boring.
10 The game feels repetitive
Some people didn't like the game because they believed that parts of it seemed repetitive and didn't contribute much to the plot.
11 The music isn't that good
While many people praised Chrono Trigger's music, others believed that the tracks weren't that good compared to the tracks of other RPGs.