We hit up TL on 5/28 and it was decently busy when we arrived around 11-ish (we had breakfast at Cake Bake after checking out of BWI). Crowds definitely increased as the day went on though, I assume from people getting in after flying or driving down as opposed to split stay guests like us. We were very glad to have booked an umbrella, though I still saw chairs available. Lots of people in the lazy river but it wasn't like, impassable and we had no issues getting the good floaties (the "chair" kind that let you sit, as opposed to the donuts). We are not really slide people but Miss Adventure Falls was a 15 min wait at one point, only because it had been down for a while. Even so, overall it still wasn't as bad as it was at BB when it was the only park open. I think having the two parks open is dispersing crowds better.
One thing I noticed about that week in general vs. many previous Memorial Day weeks is that there was next to no drop off in crowd levels anywhere the way there usually is. Usually there's a mass exodus on the holiday itself due to people going back to work/school and the rest of the week is pretty quiet until the following weekend, but that wasn't the case this year. I think it was probably due to people coming down for Epic and then coming to WDW.