I just bought a place. The basement was waterproofed by the last owner - a french drain installed under the basement floor around the perimeter, leading to a sump pump (done professionally, but no warranty I can take advantage of).
Naturally I was surprised when we had a heavy rain and I found a basement full of water. I was pretty sure I knew what happened, and when it happened again a week later, my suspicions were confirmed. The basement has three very low windows (the top of all three are at ground level) and with heavy-ish rain, all three window wells fill completely up. Two of the windows have been closed and sealed (looks like plywood was put over the window and then covered with concrete). A minuscule amount of water still seeps through one of these, but not a real problem. However, the one that is still a window ends up emptying itself into the basement.
The good news is that my property is sloped, and these are actually at the high point of my property. The bad news is that the surrounding yard (as well as part of my neighbors yard) slopes down to the house. So, the water already has somewhere to go. The issue is that it drains to the house and the runs along the house off of my property. If the rain is heavy, then some of it inevitably ends up in my window wells while it is working its way somewhere lower.
I can't decide if it would be better to build a simple "mound" running around this section of the house, so that it can't reach the actual house, or if it would be better to try to dig a drain. I suspect that something raised to divert the water would be easier - while the yard is sloped, it is gentle, so I might have to dig a long drain to get it to "empty" into a lower section of the yard.
Here is the side of the yard with the window that leaks. The water flows off "behind" me. The sandy area here is flat because there had previously been an above ground pool, but the yard rises to the left of the picture. You can actually see where the water was flowing towards the house (there is another "stream" that breaks off and flows directly behind me and down the yard without reaching to the house). A lot of water also comes down from the neighbors yard on the other side of the fence.
Here are the other two windows. These wells fill up, but the windows are fairly well sealed, so no water leaks into the basement. The ground right here has a more gentle slope, but it slopes towards the front of the house. Right around the corner of the house you can see that the yard drops off quickly (the front yard drains into a stream, and from there into a lake, so any water that gets into the front yard will be gone for my purposes).