My comment earlier about going to SF instead of SDC was not meant to say SF is better than SDC or they are the same. My point is we did in fact get SF passes this year to try it out and may or may not do SDC in 2024. I have not yet been to SF STL but have done the one in DFW and it is a fact that if your goal is to ride a lot of different coasters and rides, then SF probably beats SDC in that regard. You will find more of them at a SF park.
Six Flags St. Louis is similar to Six Flags Over Texas (in DFW) in the fact that both are original-build Six Flags parks, meaning both are among the three parks Six Flags actually built themselves. In that sense, you're already prepared too for a park layout that's a bit of a mess. It's the opposite of SDC in that if you go uphill you're going further into the park. You'll recognize some rides from Texas (Mr. Freeze and Batman are both mirrored from their Texas counterparts, they have the DC dark ride), and it can be a good park if you like wooden coasters. I'd say it's a bit more family oriented than some of the other Six Flags parks. The water park is almost certainly better than White Water-it used to be included with admission, I'm not sure if that still stands under Six Flags' current disaster of a CEO. They've been doing a fair amount of refurbishment work over the past decade, so parts of the park look reasonably nice, but it being a Six Flags park you can anticipate neglected areas as well.
THAT SAID, the coaster collection pales in comparison to SFOT and even, I'd say, to SDC, and illustrates that more is not necessarily better. Batman, Mr. Freeze, and American Thunder are great, and while I don't know that I'd say the park has anything irredeemably awful (others may disagree), the worst coasters at SFSTL are worse than the worst coasters at SDC or Worlds of Fun. Theming is muddled and confused even by Six Flags standards.
My top recommendation is to go in with modest expectations. I like the park, and think it is a bit underrated, but SFSTL has more consistently disappointed people I've tried to share it with than any other park-less because of anything the park actually did (it has decent customer service and operations by Six Flags standards), but simply because it's more modest compared to other Six Flags parks and they were expecting something more grandiose.