Math is one of those subjects where sometimes you just need to practice, and IXL possesses an extremely comprehensive range of math problems for all different grade levels. There aren't bells, whistles or flashing lights here (although my first grader gets incredibly excited when she wins a picture award for various goals). Every correct answer gets some version of "Great!" while an incorrect answer takes you to an explanation of how the problem needs to be worked out.
I personally like the points system although I see that a lot of reviewing teens are frustrated about it (the goal is to work your way up to a "proficient" score of 80 with a score of 100 equaling "mastery"). The love/hate of the scoring system may depend on your child's age and personality. My daughter finds first grade math pretty easy, and generally doesn't hit "submit" until she's confident of her answer, so IXL generally gives us just the right amount of problems (~25/topic) before she gets bored and is ready to move onto a different subject. I think that the sore point with the scoring is that kids can get to 80% (i.e. proficiency) without too much problem, but the algorithm to reach 100% (full mastery) is much more difficult. That's an intentional feature of the scoring, though. Its the judgment call of the parent/teacher which milestone to use (your kid is actually comprehending the topic pretty well if they can reach 80; if there is angst or a section is taking too long, for pity's sake just stop there).
For the most part, my family saves IXL for holidays/snow days and for when we're practicing "speed math" (although I've sought out a particular topic if my daughter's having problems with it, such as reading clocks or counting money). Typically we throw IXL on the laptop, cuddle up on the bed, pound through a few topics, and gloat over won cartoon tokens. Afterwards I feel content that the kid has happily practiced more math problems in 20-30 minutes than what she would have probably done in school.