The first two seasons are good, but the show becomes really great and starting in the third season. Earlier on the creators were restrained by a limited number of green-lit episodes and by the producers' choices to keep it more child oriented, but they got a lot more freedom to work with once the show proved itself successful financially.
It still stays the same cutesy merchandise driven loli magical girl comedy but it gets more mature and emotional, adding darker themes such as miscarriage, parental abuse/neglect, cultural/racial/religious prejudice, sexual growth, social anxiety, depression, death, etc.
It never gets too dark though, it always stays funny and heartwarming while still handling the darker themes tastefully and maturely.
If you enjoy the first season then continue, it gets much better in every way. Pic related, you won't get a taste of sweet Momoko until season 3.